Distributed Optimization

Case Study: ALADIN

  • Aadharsh Aadhithya A
  • Abhinesh S
  • Akshaya J
  • Jayanth Mohan
  • Vishnu Radhakrishnan

Team 01

  1. Duality
  2. Dual Ascent
  3. Dual Decomposition
  4. Method of Multipliers (MM)
  5. ADMM
  6. Parallel ADMM
  7. ALADIN: Overview
  8. ALADIN: A Walkthrough
  9. Case Study: ALADIN for Sensor Network Localization
  10. Case Study: ALADIN for learning problems

Whats waiting?

Duality

 principle of duality states that any optimization problems can be viewed from either of the two perspectives, the primal form or the dual form. If the primal is a minimization problem then the dual is a maximization problem and vice-versa.

Duality Principle

Duality gap represents the difference between the values obtained on solving the primal form and the solution obtained on solving the dual for of the same optimization problem.

 

DUAL GAP


Solving an optimization problem in it’s dual form is more preferable that solving it in it’s dual form because, The dual problem is always a convex optimization problem, even if the problem is not convex in it’s primal form.

 

Why Dual form?

 

Slater's theorem provides a sufficient condition for strong duality to hold. Namely, if

 

  • 1.)The primal problem is convex;

  • 2.)It is strictly feasible, that is, there exists

 

Slater's sufficient condition for strong duality

Dual Ascent

Dual Ascent

  • Based on the fact that dual problem is always convex/concave

Dual Ascent

  • Based on the fact that dual problem is always convex/concave
  • Solving the dual problem, helps us iteratively drive the primal towards optimality.

Dual Ascent

  • Based on the fact that dual problem is always convex/concave
  • Solving the dual problem, helps us iteratively drive the primal towards optimality.

Dual Ascent

  • Solving the dual problem, helps us iteratively drive the primal towards optimality.
\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
x \in R^n ,\,\, A \in R^{m \times n} \, \, b ,\, \lambda \in R^m

where m is number of constraints, and n is dimention of x

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
g(\lambda) = \inf_x L(x,\lambda)

What is infimum?🤔

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
g(\lambda) = \inf_x L(x,\lambda)

What is infimum?🤔

Lowerbound!

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
g(\lambda) = \inf_x L(x,\lambda)

What is infimum?🤔

\sup_\lambda g(\lambda) = \sup_\lambda \inf_x L(x,\lambda)

Find the tightest lowerbound!

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)

What is infimum?🤔

\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)

Gradient direction in the direction of increase in function.

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)

What is infimum?🤔

\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)

Gradient direction in the direction of increase in function.

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
(Ax_0-b)
\lambda_0
\text{assume } x_0, \lambda_0

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
(Ax_0-b)
\lambda_0
\text{assume } \lambda_0
\nabla_\lambda L(x_0,\lambda) = A x_0 - b
x_0 = arg \min_x L(x,\lambda_0)

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
\alpha (Ax_0-b)
\lambda_0
\text{assume } \lambda_0
\nabla_\lambda L(x_0,\lambda) = A x_0 - b
\lambda_1 = \lambda_0 + \alpha ( \nabla_\lambda L )
\lambda_0 + \alpha(A x_0 - b)
x_0 = arg \min_x L(x,\lambda_0)

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
\alpha (Ax_0-b)
\lambda_0
\text{assume } \lambda_0
\nabla_\lambda L(x_0,\lambda) = A x_0 - b
\lambda_1 = \lambda_0 + \alpha ( \nabla_\lambda L )
\lambda_0 + \alpha(A x_0 - b)
x_0 = arg \min_x L(x,\lambda_0)

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
\alpha (Ax_0-b)
\lambda_0
\text{assume } \lambda_0
\nabla_\lambda L(x_i,\lambda) = A x_i - b
\lambda_{i+1} = \lambda_i + \alpha ( \nabla_\lambda L )
\lambda_0 + \alpha(A x_0 - b)
x_i = arg \min_x L(x,\lambda_i)

Dual Ascent

\begin{aligned} \min f(x) \\ s.t Ax=b \end{aligned}
L(x,\lambda) = f(x) + \lambda^T \cdot (Ax-b)
\frac{\partial L(x,\lambda)}{\partial \lambda} = (Ax-b)
\alpha (Ax_0-b)
\lambda_0
\text{assume } \lambda_0
\nabla_\lambda L(x_i,\lambda) = A x_i - b
\lambda_{i+1} = \lambda_i + \alpha ( \nabla_\lambda L )
\lambda_0 + \alpha(A x_0 - b)
x_i = arg \min_x L(x,\lambda_i)

Repeat till Convergence

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
x = \begin{bmatrix} x_1^T && x_2^T && \cdots \cdots && x_N^T \end{bmatrix}
x_i \in R^{n_i}
x \in R^{\sum_i^N n_i}
f_i : R^{n_i} \rightarrow R
f : R^{\sum_i n_i} \rightarrow R

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
x = \begin{bmatrix} x_1^T && x_2^T && \cdots \cdots && x_N^T \end{bmatrix}
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
f_i : R^{n_i} \rightarrow R
R^{n_i}
R^m

m is number of constraints

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
f_i : R^{n_i} \rightarrow R
R^{n_i}
R^m

m is number of constraints

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
f_i : R^{n_i} \rightarrow R
R^{n_i}
R^m

m is number of constraints

R^{m \times n_i}

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
R
R
L_i : (R^{n_i} \times R^m) \rightarrow R

m is number of constraints

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
s.t A_1 x_1 = \frac{1}{N}b
s.t A_2 x_2 = \frac{1}{N}b
s.t A_n x_n = \frac{1}{N}b

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
s.t A_1 x_1 = \frac{1}{N}b
s.t A_1 x_1 = \frac{1}{N}b
s.t A_1 x_1 = \frac{1}{N}b

N subproblems can be solved in parallel

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
s.t A_1 x_1 = \frac{1}{N}b
s.t A_1 x_1 = \frac{1}{N}b
s.t A_1 x_1 = \frac{1}{N}b
\nabla_\lambda L = (\sum_i A_i x_i - b )

Dual Decomposition

\text{f is seperable}
f(x) = f_1(x_1) + f_2(x_2) \cdots f_N(x_N)
\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L(x,\lambda) = L_1(x_1, \lambda) + L_2(x_2, \lambda) \cdots L_N(x_N, \lambda) - y^T b
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
s.t A_1 x_1 = \frac{1}{N}b
s.t A_2 x_2 = \frac{1}{N}b
s.t A_n x_n = \frac{1}{N}b
\nabla_\lambda L = (\sum_i A_i x_i - b )
\lambda_{i+1} = \lambda_i + \alpha \cdot (\nabla_\lambda L)

Dual Decomposition

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
\nabla_\lambda L = (\sum_i A_i x_i - b )
\lambda_{i+1} = \lambda_i + \alpha \cdot (\nabla_\lambda L)
x_i = arg \min_{x_i} L_i(x_i,\lambda^k)

Can be carried out in parallel

Dual Decomposition

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
\nabla_\lambda L = (\sum_i A_i x_i - b )
\lambda^{k+1} = \lambda^k + \alpha \cdot (\nabla_\lambda L)
x_i = arg \min_{x_i} L_i(x_i,\lambda_k)

Can be carried out in parallel

Dual Decomposition

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L_i(x_i,\lambda) = f_i(x_i) + \lambda^T (A_i x_i)
\nabla_\lambda L = (\sum_i A_i x_i - b )
\lambda^{k+1} = \lambda^k + \alpha \cdot (\nabla_\lambda L)
x_i = \min_{x_i} L_i(x_i,\lambda_k)

Can be carried out in parallel

Repeat till convergence

Method Of Multipliers

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L = f(x) + \lambda^T(Ax-b)

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L = f(x) + \lambda^T(Ax-b)
L_{\rho}= f(x) + \lambda^T(Ax-b) + \frac{\rho}{2} \| Ax-b \|_2^2

Agumented Lagrangian

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L = f(x) + \lambda^T(Ax-b)
L_{\rho}= f(x) + \lambda^T(Ax-b) + \frac{\rho}{2} \| Ax-b \|_2^2

Agumented Lagrangian

More Robust

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L = f(x) + \lambda^T(Ax-b)
L_{\rho}= f(x) + \lambda^T(Ax-b) + \frac{\rho}{2} \| Ax-b \|_2^2
\nabla_\lambda L_\rho = ( A x - b )
\lambda_{i+1} = \lambda_i + \alpha \cdot (\nabla_\lambda L_\rho)

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L_{\rho} (x,\lambda) = f(x) + \lambda^T(Ax-b) + \frac{\rho}{2} \| Ax-b \|_2^2
\nabla_\lambda L_\rho = ( A x^* - b )
\lambda_{i+1} = \lambda_i + \rho \cdot (\nabla_\lambda L_\rho)
\text{assume } \lambda_0
x* = arg \min L_\rho (x,\lambda_i)

Method Of Multipliers

\begin{aligned} \min_x f(x)\\ st \,\, Ax=b \end{aligned}
L_{\rho} (x,\lambda) = f(x) + \lambda^T(Ax-b) + \frac{\rho}{2} \| Ax-b \|_2^2
\nabla_\lambda L_\rho = ( A x^* - b )
\lambda_{i+1} = \lambda_i + \rho \cdot (\nabla_\lambda L_\rho)
\text{assume } \lambda_0
x* = arg \min L_\rho (x,\lambda_i)

Repeat till convergence

ADMM

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
x \in R^{n_x}, \, \, z \in R^{n_z}

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
x \in R^{n_x}, \, \, z \in R^{n_z}
A \in R^{m \times n_x} \, \, B \in R^{m \times n_z}
m \rightarrow \text{number of constraints}

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
assume \, \, x,z,\lambda

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
assume \, \, x,z,\lambda
x^{k+1} = arg \min_x L_\rho (x,z^k , \lambda^k, \rho)

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
assume \, \, x,z,\lambda
x^{k+1} = arg \min_x L_\rho (x,z^k , \lambda^k, \rho)
z^{k+1} = arg \min_z L_\rho (x^{k+1},z , \lambda^k, \rho)

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
assume \, \, x,z,\lambda
x^{k+1} = arg \min_x L_\rho (x,z^k , \lambda^k, \rho)
z^{k+1} = arg \min_z L_\rho (x^{k+1},z , \lambda^k, \rho)
\lambda^{k+1} = \lambda^k + \rho (\nabla_\lambda L_\rho (x^{k+1}, z^{k+1},\lambda^k,\rho))

ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
assume \, \, x,z,\lambda
x^{k+1} = arg \min_x L_\rho (x,z^k , \lambda^k, \rho)
z^{k+1} = arg \min_z L_\rho (x^{k+1},z , \lambda^k, \rho)
\lambda^{k+1} = \lambda^k + \rho (\nabla_\lambda L_\rho (x^{k+1}, z^{k+1},\lambda^k,\rho))

Repeat till convergence

Parallel ADMM

Parallel ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2

Parallel ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
A=I,B=-I,c=0

Parallel ADMM

\min f(x) + g(z)
S.T \,\, Ax+Bz=c
L_\rho = f(x) + g(z) + \lambda^T (Ax+Bz-c) + \frac{\rho}{2} \| Ax+Bz-c\|^2_2
A=I,B=-I,c=0
L_\rho = f(x) + g(z) + \lambda^T (x-z) + \frac{\rho}{2} \| x-z\|^2_2

Parallel ADMM

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} (x_i - z_i) + \frac{\rho}{2}(\| A_i (x_i - z_i^k)\|_2^2)
z_i^{k+1} = arg \min_z \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| A_i (x_i^{k+1} - z_i)\|_2^2
x_1
x_1
x_2
x_3
z

Parallel ADMM

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} ( x_i - z_i) + \frac{\rho}{2}(\| A_i (x_i - z_i^k)\|_2^2)
\frac{\partial L_\rho}{\partial z}
z_i^{k+1} = arg \min_z \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| A_i (x_i^{k+1} - z_i)\|_2^2

Parallel ADMM

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} (x_i - z_i) + \frac{\rho}{2}(\| (x_i - z_i^k)\|_2^2)
\lambda_i^{k+1} = \lambda_i^{k} + \rho (x_i^{k+1} - z_i^{k+1})
z_i^{k+1} = arg \min_z \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| (x_i^{k+1} - z_i)\|_2^2

Parallel ADMM

z^{k+1} = \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| A_i (x_i^{k+1} - z_i)\|_2^2
\lambda_i^{k+1} = \lambda_i^{k} + \rho A_i (x_i^{k+1} - z_i^{k+1})

Can be carried out in parallel

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} (x_i - z_i) + \frac{\rho}{2}(\| A_i (x_i - z_i^k)\|_2^2)

Parallel ADMM

z^{k+1} = \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| A_i (x_i^{k+1} - z_i)\|_2^2
\lambda_i^{k+1} = \lambda_i^{k} + \rho A_i (x_i^{k+1} - z_i^{k+1})

Can be carried out in parallel

Centralized

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} (x_i - z_i) + \frac{\rho}{2}(\| A_i (x_i - z_i^k)\|_2^2)

Parallel ADMM

z^{k+1} = \sum_i - \lambda^{kT} A_i z_i + \frac{\rho}{2} \| A_i (x_i^{k+1} - z_i)\|_2^2
\lambda_i^{k+1} = \lambda_i^{k} + \rho A_i (x_i^{k+1} - z_i^{k+1})

Can be carried out in parallel

Centralized

x_i^{k+1} = arg \min f_i(x_i) + \lambda_i^{kT} (x_i - z_i) + \frac{\rho}{2}(\| A_i (x_i - z_i^k)\|_2^2)

Solve NLP

Solve QP

Update 

How QP?🤔

ALADIN

Augmented Lagrangian Based Alternating Direction Inexact Newton

Overview of ALADIN

Overview of ALADIN

Agumented Lagrangian

x^* = arg \min_x f(x) + \lambda^T c(x) + \frac{\rho}{2}|c(x)\|_2^2

Overview of ALADIN

Solve NLPs of the form

In Parallel

x^* = arg \min_x f(x) + \lambda^T c(x) + \|c(x)\|_2^2

For N subproblems, we should solve N different NLP's in parallel

Overview of ALADIN

x^* = arg \min_x f(x) + \lambda^T c(x) + \|c(x)\|_2^2
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)

Overview of ALADIN

x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2

Overview of ALADIN

x_i^* , \nabla f(x_i^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2

Linear Approximation of Constraints,

\hat{c}

Overview of ALADIN

x_i^* , \nabla f(x_i^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2

Linear Approximation of Constraints,

\hat{c}

Solve Coordinated QP.

(Centralized)

Overview of ALADIN

x_i^* , \nabla f(x_i^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2

Linear Approximation of Constraints,

\hat{c}

Solve Coordinated QP.

(Centralized)

Solve NLPs.

(Parallel)

Overview of ALADIN

x_i^* , \nabla f(x_i^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
x^* , \nabla f(x^*) , \nabla_{xx}^2 \mathscr(L)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2

Linear Approximation of Constraints,

\hat{c}

Solve Coordinated QP.

(Centralized)

Solve NLPs.

(Parallel)

Update x and lambda

Unconstrained Newton Methods

f(x)

Newton Methods

f(x)
f(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2 + \frac{f'''(x_0)}{3!}(x-x_0)^3 \cdots

Newton Methods

f(x)
\hat{f}(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2
x_0

Local Approximation

Around point x0

\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)

Newton Methods

f(x)
\hat{f}(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2
x_0

Local Approximation

Around point x0

\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)

Newton Methods

f(x)
\hat{f}(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2
x_0

Local Approximation

Around point x0

\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}
\hat{x}

Newton Methods

f(x)
\hat{f}(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2

Local Approximation

Around point x0

\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}
\hat{x}

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)
Ap=b
p = \hat{x}-x_0

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)
Ap=b
p = \hat{x}-x_0

If A is full Rank

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)
Ap=b
p = \hat{x}-x_0

If A is full Rank

x update is simply solving a system of Linear Equation!

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)
Ap=b
p = \hat{x}-x_0

If A is full Rank

x update is simply solving a system of Linear Equation!

Newton Methods

\hat{f}(x) = f(x_0) + \nabla_xf(x_0)(x-x_0) + \frac{\nabla_{xx}^2f(x_0)}{2!}(x-x_0)^2
\frac{d}{dx}\hat{f(x)} = f'(x_0) + f''(x_0)(x-x_0)
f'(x_0) + f''(x_0)(x-x_0)=0
\hat{x} = x_0 - \frac{f'(x_0)}{f''(x_0)}

1-D Updates

N-D Updates

\nabla\hat{f(x)} = \nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)
\nabla f(x_0) + \nabla_{xx}^2f(x_0)(x-x_0)=0
\nabla_{xx}^2f(x_0)(x-x_0)=-\nabla f(x_0)
Ap=b
p = \hat{x}-x_0

Remark!

 Newton Iteration yields the roots, while Newton iteration on the first-order necessary conditions for optimality (of second-order approximation) of F yields a stationary point.

Sequential Quadratic Programming

f(x)
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
\mathscr{L}(x,\lambda) = f(x) + \lambda^T c(x)
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
\mathscr{L}(x,\lambda) = f(x) + \lambda^T c(x)
\nabla_x \mathscr{L}(x,\lambda) = \nabla_x f(x) + \lambda^T \nabla_x c(x) = 0
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
\mathscr{L}(x,\lambda) = f(x) + \lambda^T c(x)
\nabla_x \mathscr{L}(x,\lambda) = \nabla_x f(x) + \lambda^T \nabla_x c(x) = 0
c(x)=0
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
\mathscr{L}(x,\lambda) = f(x) + \lambda^T c(x)
\nabla_x \mathscr{L}(x,\lambda) = \nabla_x f(x) + \lambda^T \nabla_x c(x) = 0
c(x)=0
\}

First Order

Optimality Conditions

\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
\mathscr{L}(x,\lambda) = f(x) + \lambda^T c(x)
\nabla_x \mathscr{L}(x,\lambda) = \nabla_x f(x) + \lambda^T \nabla_x c(x) = 0
c(x)=0
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}

Root Finding Procedures can be invoked!

\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
F(x,\lambda) +\nabla F(x,\lambda) \cdot \Delta x
f(x) = f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)}{2!}(x-x_0)^2 + \frac{f'''(x_0)}{3!}(x-x_0)^3 \cdots
\}
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
F(x,\lambda) +\nabla F(x,\lambda) \cdot \Delta x =0
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
F(x,\lambda) +\nabla F(x,\lambda) \cdot \Delta x =0
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\nabla F(x,\lambda) = \begin{bmatrix} \frac{\partial \left(\nabla_x \mathscr{L}(x,\lambda) \right)}{\partial x} & \frac{\partial c(x)}{\partial x} \\ \frac{\partial \left ( \nabla_x \mathscr{L}(x,\lambda) \right)}{\partial \lambda} & \frac{\partial c(x)}{\partial \lambda} \end{bmatrix}
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\nabla F(x,\lambda) = \begin{bmatrix} \frac{\partial \left(\nabla_x \mathscr{L}(x,\lambda) \right)}{\partial x} & \frac{\partial c(x)}{\partial x} \\ \frac{\partial \left ( \nabla_x \mathscr{L}(x,\lambda) \right)}{\partial \lambda} & \frac{\partial c(x)}{\partial \lambda} \end{bmatrix}
\nabla_x \mathscr{L}(x,\lambda) = \nabla_x f(x) + \lambda^T \nabla_x c(x)
\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\nabla F(x,\lambda) = \begin{bmatrix} \nabla_{xx}^2 \mathscr{L}(x,\lambda) & \nabla_x c(x)^T \\ \nabla_x c(x) & 0 \end{bmatrix}
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\mathscr{L} = \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) + \lambda^T (\nabla c(x_k) p + c(x_k))
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\mathscr{L} = \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) + \lambda^T (\nabla c(x_k) p + c(x_k))
\frac{\partial \mathscr{L}}{\partial p} = \nabla_{xx}^2 L_k p + \nabla f(x_k) + \lambda^T (\nabla c(x_k) ) = 0
\nabla c(x_k) p + c(x_k) = 0
\}

First Order

Optimality Conditions

\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\nabla_{xx}^2 L_k p + \lambda^T (\nabla c(x_k) ) = -\nabla f(x_k)
\nabla c(x_k) p = -c(x_k)
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\nabla_{xx}^2 L_k p + \lambda^T (\nabla c(x_k) ) = -\nabla f(x_k)
\nabla c(x_k) p = -c(x_k)
\begin{bmatrix} \nabla_{xx}^2 L_k & (\nabla c(x_k) \\ \nabla c(x_k) & 0 \\ \end{bmatrix} \begin{bmatrix} p \\ \lambda \end{bmatrix} = \begin{bmatrix} -\nabla f(x_k) \\ -c(x_k) \end{bmatrix}
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
\begin{bmatrix} \nabla_{xx}^2 L_k & (\nabla c(x_k) \\ \nabla c(x_k) & 0 \\ \end{bmatrix} \begin{bmatrix} p \\ \lambda \end{bmatrix} = \begin{bmatrix} -\nabla f(x_k) \\ -c(x_k) \end{bmatrix}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\equiv
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
\begin{bmatrix} \nabla_{xx}^2 L_k & (\nabla c(x_k) \\ \nabla c(x_k) & 0 \\ \end{bmatrix} \begin{bmatrix} p \\ \lambda \end{bmatrix} = \begin{bmatrix} -\nabla f(x_k) \\ -c(x_k) \end{bmatrix}

Iteratively Solve till convergence

Sequential Quadratic Programming(SQP)

S.T \, \, \nabla c(x_k) p + c(x_k) = 0
\begin{aligned} \underset{p}{\min} \,\, \frac{1}{2} p^T \nabla_{xx}^2 L_k p + \nabla f(x_k)^T p + f(x_k) \end{aligned}
\begin{bmatrix} \nabla_{xx}^2 L_k & (\nabla c(x_k) \\ \nabla c(x_k) & 0 \\ \end{bmatrix} \begin{bmatrix} p \\ \lambda \end{bmatrix} = \begin{bmatrix} -\nabla f(x_k) \\ -c(x_k) \end{bmatrix}

Sequential Quadratic Programming(SQP)

S.T \, \, \nabla c(x_k) p + c(x_k) = 0

Equivalent Second-order Approximation of the Lagrangian

Equivalent First-order Approximation of the Constraints

\begin{aligned} \min f(x)\\ s.t\,\, c(x)=0 \end{aligned}
F(x,\lambda) = \begin{bmatrix} \nabla_x f(x) + \lambda^T \nabla_x c(x) \\ c(x) \end{bmatrix} = \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\nabla F(x,\lambda) \cdot \Delta x = -F(x,\lambda)
\nabla F(x,\lambda) = \begin{bmatrix} \frac{\partial \left ( \nabla_x f(x) + \lambda^T \nabla_x c(x) \right )}{\partial x} & \frac{\partial c(x)}{\partial x} \\ \frac{\partial \left ( \nabla_x f(x) + \lambda^T \nabla_x c(x) \right ) }{\partial \lambda} & \frac{\partial c(x)}{\partial \lambda} \end{bmatrix}

ALADIN: A walkthrough

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2 \cdots x_n} \sum_i^n f_i(x_i,p_i)\\ S.T \,\, g_i(x_i,p_i)=0 \\ h_i(x_i,p_i) \leq 0 \\ x_{lb}^i \leq x_i \leq x_{ub}^i \\ \sum_i^n A_i \cdot x_i = b \end{aligned}

Typicall Form of a distributed optimization problem

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2 \cdots x_n} \sum_i^ns f_i(x_i,p_i)\\ S.T \,\, g_i(x_i,p_i)=0 \\ h_i(x_i,p_i) \leq 0 \\ x_{lb}^i \leq x_i \leq x_{ub}^i \\ \sum_i^n A_i \cdot x_i = b \end{aligned}

Typicall Form of a distributed optimization problem

Other formulations can be casted into the above formulation by introducing auxiliary variables.

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2 \cdots x_n} \sum_i^ns f_i(x_i,p_i)\\ S.T \,\, g_i(x_i,p_i)=0 \\ h_i(x_i,p_i) \leq 0 \\ x_{lb}^i \leq x_i \leq x_{ub}^i \\ \sum_i^n A_i \cdot x_i = b \end{aligned}

Typicall Form of a distributed optimization problem

Other formulations can be casted into the above formulation by introducing auxiliary variables.

Box Constraint

Solvers, typically have spealized numerical routines to handle box constraints, which improves the efficiency of the solver

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

Non-Convex Constraints

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

Non-Convex Constraints

x = \begin{bmatrix} x1 \\ x2 \end{bmatrix} \in R^2
2 \cdot (x-1)^2
(x-2)^2

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

x = \begin{bmatrix} x1 \\ x2 \end{bmatrix} \in R^2
2 \cdot (x-1)^2
(x-2)^2
2 \cdot (x-1)^2
(x-2)^2

+

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

x = \begin{bmatrix} x1 \\ x2 \end{bmatrix} \in R^2
2 \cdot (x-1)^2
(x-2)^2

+

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

2 \cdot (x-1)^2
(x-2)^2

+

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

1.5
-1
x_1 \cdot x_2

ALADIN: A walkthrough

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

ALADIN: A walkthrough

\begin{aligned} -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Example Problem

ALADIN: A walkthrough

Example Problem

ALADIN: A walkthrough

Example Problem

x_1 = 0.81 , x_2 = 1.83

Centralized Solution

ALADIN: A walkthrough

Example Problem

Centralized Solution

import casadi.*
x1 = SX.sym('x1');
x2 = SX.sym('x2');

nlp = struct('x', [x1;x2], 'f', 2*(x1 - 1)^2 + (x2 - 2)^2, 'g', x1 * x2);
S = nlpsol('S', 'ipopt', nlp);

sol = S('x0', [0, 0], 'lbg', -1, 'ubg', 1.5);
x_1 = 0.81 , x_2 = 1.83

ALADIN: A walkthrough

Example Problem

Distributed Optimization

To apply any distributed optimization, the objective function and constraints needs to be decoupled.

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Only in terms of x1

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Only in terms of x1

Only in terms of x2

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Only in terms of x1

Only in terms of x2

Complicating Constraint

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Only in terms of x1

Only in terms of x2

Complicating Constraint

A Complicating Constraint is a constraint that, if relaxed, the problem becomes decoupled

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Only in terms of x1

Only in terms of x2

Complicating Constraint

A Complicating Constraint is a constraint that, if relaxed, the problem becomes decoupled

Task: Decouple the Problem Formulation

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
x_1 \rightarrow y_1
x_2 \rightarrow y_2 \rightarrow \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}
y_1 \in R \,\, y_2 \in R^2

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}

Use y21 as a "proxy"  for y1 within subsystem 2

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}

Use y21 as a "proxy"  for y1 within subsystem 2

To do this, set y1 to be equal to y21

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}

Without Loss of generality write,

A_1 y_1 + A_2 y_2 = b

Choose appropriate values of A1, A2,b

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}

Without Loss of generality write,

A_1 y_1 + A_2 y_2 = b
A_1 \in R \,\, A_2 \in R^{1 \times 2}

Take hint from dimentions

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}

Without Loss of generality write,

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
b \in R

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}
x_1 x_2 \geq -1
x_1 x_2 \leq 1.5

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}
x_1 x_2 \geq -1
x_1 x_2 \leq 1.5
y_1 y_{22} \geq -1
y_1 y_{22} \leq 1.5

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}
x_1 x_2 \geq -1
x_1 x_2 \leq 1.5
y_1 y_{22} \geq -1
y_1 y_{22} \leq 1.5
y_{21} y_{22} \geq -1
y_{21} y_{22} \leq 1.5

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{x_1,x_2} 2 \cdot (x_1 - 1)^2 + (x_2 - 2)^2\\ S.T -1 \leq x_1 \cdot x_2 \leq 1.5 \end{aligned}

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
y_1
\begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix}
y_{21} y_{22} \geq -1
y_{21} y_{22} \leq 1.5

By setting a proxy variable, our constraints are now in terms of only y2. Hence the complicating constraint is removed with help of y1=y21

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
\begin{aligned} \min_{y_1,y_2} 2 \cdot (y_1 - 1)^2 + (y_{22} - 2)^2\\ S.T -1 \leq y_{21} \cdot y_{22} \leq 1.5 \end{aligned}

Only in terms of y2

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

Now we can write Constraints in terms of Proxy variable from subsystem 2

1 \cdot y_1 + \begin{bmatrix} -1 & 0\end{bmatrix} \cdot \begin{bmatrix} y_{21} \\ y_{22}\end{bmatrix} = 0
\begin{aligned} \min_{y_1,y_2} 2 \cdot (y_1 - 1)^2 + (y_{22} - 2)^2\\ S.T -1 \leq y_{21} \cdot y_{22} \leq 1.5 \end{aligned}

Only in terms of y2

This kind of constraint is called affine coupling constraints/ Consensus constraints. They help us decompose the problem

Notice the extra set

of constraints

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

Now we can write Constraints in terms of Proxy variable from subsystem 2

\sum_i A_i \cdot y_i = 0
\begin{aligned} \min_{y_1,y_2} 2 \cdot (y_1 - 1)^2 + (y_{22} - 2)^2\\ S.T -1 \leq y_{21} \cdot y_{22} \leq 1.5 \end{aligned}
A_1 = 1 \,\, A_2 = \begin{bmatrix} -1 & 0\end{bmatrix}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

Task: Decouple the Problem Formulation

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
+
H_2 \leq 0

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\| x \|_\Sigma = \sqrt{x^T \Sigma x} \,\, x\succcurlyeq0

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\| x \|_\Sigma = \sqrt{x^T \Sigma x} \,\, \Sigma \succcurlyeq0
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\rho=100
z_1 = 0
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\lambda = 0

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1,y_2} f_1(y_1) + f_2 (y_2)\\ S.T H_2(y_2) \leq 0 \\ A_1y_1 + A_2 y_2 = 0 \end{aligned}
\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\rho=100
z_1 = 0
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\lambda = 0

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\rho=100
z_1 = 0
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
\lambda = 0
\frac{\partial \mathscr{L}}{\partial x} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial x} = 0 \implies y_1^* = \frac{4}{104} = 0.0385
s.t\,\, y_2 \in \mathscr{X}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
\rho=100
z_1 = 0
\lambda = 0
\frac{\partial \mathscr{L}}{\partial x} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial x} = 0 \implies y_1^* = \frac{4}{104} = 0.0385

Gradient of Objective

\nabla \,\, 2(y_1 - 1)^2 = 4(y_1 - 1)

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
\rho=100
z_1 = 0
\lambda = 0
\frac{\partial \mathscr{L_1}}{\partial y_1} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial y_1} = 0 \implies y_1^* = \frac{4}{104} = 0.0385

Gradient of Objective

\nabla \,\, 2(y_1 - 1)^2 = 4(y_1 - 1)
\nabla \,\, f_1(y_1*) = 4(0.0385 - 1) = -3.86

Hessian of Objective

\nabla^2 \,\, 2(y_1 - 1)^2 = \nabla 4(y_1 - 1) = 4

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
\rho=100
z_1 = 0
\lambda = 0
\frac{\partial \mathscr{L_1}}{\partial y_1} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial y_1} = 0 \implies y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = 4(0.0385 - 1) = -3.86
\nabla^2 \,\, 2(y_1 - 1)^2 = \nabla 4(y_1 - 1) = 4
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
s.t\,\, y_2 \in \mathscr{X}

Solve

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
\rho=100
z_1 = 0
\lambda = 0
\frac{\partial \mathscr{L_1}}{\partial y_1} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial y_1} = 0 \implies y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = 4(0.0385 - 1) = -3.86
\nabla^2 \,\, 2(y_1 - 1)^2 = \nabla 4(y_1 - 1) = 4
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
s.t\,\, y_2 \in \mathscr{X}

Solve

y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\mathscr{L_{\rho}^1} = f_1(y_1) + \lambda^T (A_1 y_1 - 0) + \frac{\rho}{2} \| y_1 - z_1 \|^2_{\Sigma}
min_{y_1} \mathscr{L_\rho^1}
\rho=100
z_1 = 0
\lambda = 0
\frac{\partial \mathscr{L_1}}{\partial y_1} = 4(y_1 -1 ) + 100 (y_1)
\frac{\partial \mathscr{L}}{\partial y_1} = 0 \implies y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = 4(0.0385 - 1) = -3.86
\nabla^2 \,\, 2(y_1 - 1)^2 = \nabla 4(y_1 - 1) = 4
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
s.t\,\, y_2 \in \mathscr{X}

Solve

y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\lambda = 0
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
s.t\,\, y_2 \in \mathscr{X}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} \frac{\partial f_2}{\partial y_{21}} \\ \frac{\partial f_2}{\partial y_{22}} \\ \end{bmatrix} = \begin{bmatrix} 0 \\ 2*(y_{22}-2)\\ \end{bmatrix} = \begin{bmatrix} 0\\ 2*(0.039-2)=-3.92\\ \end{bmatrix}

gradient of objective

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
\lambda = 0
\mathscr{L_\rho^2} = f_2(y_2) + \lambda^T (A_2 y_2 - 0) + \frac{\rho}{2} \| y_2 - z_1 \|^2_{\Sigma}
min_{y_2} \mathscr{L_\rho^2}
\rho=100
\begin{bmatrix} z_{21} \\ z_{22} \end{bmatrix}= \begin{bmatrix} 0 \\ 0 \end{bmatrix}
s.t\,\, y_2 \in \mathscr{X}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} \frac{\partial f_2}{\partial y_{21}} \\ \frac{\partial f_2}{\partial y_{22}} \\ \end{bmatrix} = \begin{bmatrix} 0 \\ 2*(y_{22}-2)\\ \end{bmatrix} = \begin{bmatrix} 0\\ 2*(0.039-2)=-3.92\\ \end{bmatrix}

gradient of objective

hessian of objective

\nabla^2 f_2(y_2) = \begin{bmatrix} \frac{\partial f_2}{\partial y_{21} \partial y_{21}} & \frac{\partial f_2}{\partial y_{22} \partial y_{21}} \\ \frac{\partial f_2}{\partial y_{21} \partial y_{22}} & \frac{\partial f_2}{\partial y_{22} \partial y_{21}}\\ \end{bmatrix} = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
bQP = -y_1*

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
bQP = -y_1*

Casadi

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
dx
x_i = x_i+dx_i
\lambda = \lambda + \rho (\sum_i A_i x_i - b )

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
x_1 = 0.0385 + 0.965 = 1.0035

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
y_1 = 0.0385 + 0.965 = 1.0035
y_2 = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix} + \begin{bmatrix} 1 \\ 1.96 \end{bmatrix} = \begin{bmatrix} 1 \\ 2.39 \end{bmatrix}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
y_1 = 0.0385 + 0.965 = 1.0035
y_2 = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix} + \begin{bmatrix} 1 \\ 1.96 \end{bmatrix} = \begin{bmatrix} 1 \\ 2.39 \end{bmatrix}

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
y_1 = 0.0385 + 0.965 = 1.0035
y_2 = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix} + \begin{bmatrix} 1 \\ 1.96 \end{bmatrix} = \begin{bmatrix} 1 \\ 2.39 \end{bmatrix}
\sum_i A_i y_i - 0 = 1 y_1 + \begin{bmatrix} -1 && 0 \end{bmatrix} y_2 = 0.0035

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
HQP =
\nabla^2 \,\, f_1(y_1)
\nabla^2 f_2(y_2) =
gQP =
\nabla \,\, f_1(y_1*)
\nabla f_2(y_2)
\begin{aligned} \underset{p}{\min} \,\, \sum_i^N \frac{1}{2} p_i^T \nabla_{xx}^2 L_k^i p_i + \sum_i^N\nabla f(x^i_k)^T p + \sum_i^N f(x^i_k) \end{aligned}
S.T \, \, \nabla c(x_k) p + c(x_k) = 0
+ \lambda^T\hat{c}(x_k) + \|\hat{c}(x_k^i)\|^2
0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
y_1 = 0.0385 + 0.965 = 1.0035
y_2 = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix} + \begin{bmatrix} 1 \\ 1.96 \end{bmatrix} = \begin{bmatrix} 1 \\ 2.39 \end{bmatrix}
\sum_i A_i y_i - 0 = 1 y_1 + \begin{bmatrix} -1 && 0 \end{bmatrix} y_2 = 0.0035
\lambda = \lambda + 100 \cdot (0.0035) = 0.35

ALADIN: A walkthrough

Example Problem

Distributed Optimization

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}
y_2^* = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix}
g_1
g_2
g_1: -1
g_2: -1.5

Constraints not active

\nabla f_2(y_2) = \begin{bmatrix} 0\\ -3.92\\ \end{bmatrix}
\nabla^2 f_2(y_2) = \begin{bmatrix} 0 & 0\\ 0 & 2\\ \end{bmatrix}
y_1^* = \frac{4}{104} = 0.0385
\nabla \,\, f_1(y_1*) = -3.86
\nabla^2 \,\, f_1(y_1) = 4
dx_i = 0.965 , \begin{bmatrix} 1 \\ 1.96 \end{bmatrix}
y_1 = 0.0385 + 0.965 = 1.0035
y_2 = \begin{bmatrix} 0 \\ 0.39 \end{bmatrix} + \begin{bmatrix} 1 \\ 1.96 \end{bmatrix} = \begin{bmatrix} 1 \\ 2.39 \end{bmatrix}
\sum_i A_i y_i - 0 = 1 y_1 + \begin{bmatrix} -1 && 0 \end{bmatrix} y_2 = 0.0035
\lambda = \lambda + 100 \cdot (0.0035) = 0.35
\text{End of iteration 1}

Updates

ALADIN: A walkthrough

Example Problem

Convergence

\begin{aligned} \min_{y_1} 2(y_1-1)^2 \\ A_1 y_1 = 0 \end{aligned}
\begin{aligned} \min_{y_2} (y_{22}-2)^2 \\ S.T -1 - y_{21}y_{22}\leq 0 \\ -1.5 + y_{21}y_{22} \leq 0 \\ A_2 y_2 = 0 \end{aligned}

Application of ALADIN in "Classification Problems in Machine Learning"

Problem Goal

To find a suitable parameter w that can classify the input data into its label

Problem Setup

N  = number of input data

       = dimension of input data

            = number of subsystems

cap = capacity of each subsystem

gamma = hyperparameter

x, y = data ,label  

     = decison variable

 

n_x
N_{subs}
\omega

Loss Function

\min_{x\epsilon R^d } \;f\left(\omega \right)=\frac{1}{N}\sum_{j=1}^N \log \left(1+e^{-y_i x_j^T \omega } \right)+\frac{\gamma }{2}\;||\omega ||_2^2

L-2 Regularised Loss Function

Input Data

  • ML_data.mat
  • In this example we have have taken 10 subsystems 

Implementation Using Aladin-

\alpha

Algorithm Convergence

Inference

  • ALADIN converges after 5 iterations
  • As observed in the graph the y residue log|Ax-b| converges to a value
  • As we proceed in the iterations the value of x does not chnage 

Application of ALADIN in "Sensor Network Localization"

Problem SETUP

N = number of sensors present in the network

                                  is the unknown position of sensor 'i'

           the estimated position of sensor 'i' by itself

           the estimated position of sensor 'i+1' by sensor 'i'

           estimated distance between sensor 'i' and it's neighbours.

\eta_i =
X_i = (x_i,y_i)^T \epsilon R^2
\xi_i =
\overline\eta_i =
S_7
S_1
S_2
S_3
S_5
S_5
S_6

DECOUPLED CASE

Each sensor takes a measurement      of its position

\eta_i
X_i
\forall i \epsilon {1,2,3,...,7}\;\;\; \underset{x_i}{min} \; ||X_i - \eta_i||_2^2
S_7
S_1
S_2
S_3
S_5
S_5
S_6

COUPLED CASE

sensors additionally measure the distance to their neighbors

\underset{X}{min} \sum_{i=1}^{7} (||X_i - \eta_i||_2^2 + ||X_i - X_i+1||_2 + \overline{\eta_i}^2)

EQUIVALENCE FORMULATION

x_1 = (X_1,\xi_1) \;\;\;\forall\;\;\; \xi_1 = X_2\\ x_2 = (X_2,\xi_2) \;\;\;\forall\;\;\; \xi_2 = X_3\\ x_2 = (X_3,\xi_3) \;\;\;\forall\;\;\; \xi_3 = X_4\\ x_2 = (X_4,\xi_4) \;\;\;\forall\;\;\; \xi_4 = X_5\\ x_2 = (X_5,\xi_5) \;\;\;\forall\;\;\; \xi_5 = X_6\\ x_2 = (X_6,\xi_6) \;\;\;\forall\;\;\; \xi_6 = X_7\\ x_2 = (X_7,\xi_7) \;\;\;\forall\;\;\; \xi_7 = X_1\\
\xi_i = X_{i+1}

using Affine Coupling, the above constraint can be written as 

\sum_{i=1}^{7} \; A_i.x_i = 0 \;\;\forall\;\; x_i = (X_i,\xi_i)

COMPLETE FORMULATION OF
SENSOR LOCALIZATION PROBLEM

\underset{x}{min} \;\; f_i(x_i)\\ subject\;to\; \sum_{i=1}^{7} A_i.x_i = 0
f_i(x_i) = \frac{1}{2} ||X_i-\eta_i||_2^2 + \frac{1}{2}||\xi_i + \eta_{i_1}||_2^2 + \frac{1}{2}(||X_i - \xi_i||_2-\overline\eta_i)^2

GENERALIZATION OF THE SENSOR MINIMIZATION PROBLEM

\begin{array}{l} \min_x \sum_{i=1} f_i \left(x_i \right)\\ s\ldotp t\ldotp {\;\;\;\;\;h}_i \left(x_i \right)\le 0\;\;\;\;\;\forall \;\;\;i\epsilon \left\lbrace 1,\ldotp \ldotp \ldotp \ldotp \ldotp \ldotp \ldotp ,N\right\rbrace \\ \;\;\;\;\;\;\;\;\;\;\;\;\;\xi_i =x_{i+1} \;\;\;\;\;\;\;\forall \;\;\;i\epsilon \left\lbrace 1,\ldotp \ldotp \ldotp \ldotp \ldotp \ldotp \ldotp ,N\right\rbrace \\ \mathrm{with},\\ f_i \left(x_i \right)=\frac{1}{4\sigma_i^2 }||X_i -n_i ||_2^2 \;+\frac{1}{4\sigma_{i+1}^2 }||\xi_i \;-\eta_{i+1} ||_2^2 +\frac{1}{2\sigma_{i+1}^2 }{\left(||X_i -\xi_i ||_2^2 -\bar{\eta_i } \right)}^2 \\ h_i \left(x_i \right)={\left(||X_i -\xi_i ||_2^2 -\bar{\eta_i } \right)}^2 -\overline{\sigma_i^2 } \end{array}

INITIAL ASSUMPTION

All the sensors present in the network are aligned along a circle

X_i =\left(N\;\cos \left(\frac{2i\pi }{N}\right),N\;\sin \left(\frac{2i\pi }{N}\right)\right)
function [eta,eta_bar] = getEta(N, d, sigma)
% returns by sensor estimated initial position and distance to its neighbours
 
 eta     = zeros(d, N + 1);
 eta_bar = zeros(1, N);
 
 for i = 1 : N
     eta( :, i ) = [N * cos(2 * i * pi / N) + normrnd(0, sigma) ; ...
                    N * sin(2 * i * pi / N) + normrnd(0, sigma)];
     
     eta_bar(i)  = 2 * N * sin( pi / N) + normrnd(0, sigma);
 end
 
 eta(:, N + 1) = eta(:, 1);
end

IMPLEMENTATION OF THE OBJECTIVE FUNCTION AND INEQUALITY CONSTRAINTS IN MATLAB

f_i \left(x_i \right)=\frac{1}{4\sigma_i^2 }||X_i -n_i ||_2^2 \;+\frac{1}{4\sigma_{i+1}^2 }||\xi_i \;-\eta_{i+1} ||_2^2 +\frac{1}{2\sigma_{i+1}^2 }{\left(||X_i -\xi_i ||_2^2 -\bar{\eta_i } \right)}^2 \\ h_i \left(x_i \right)={\left(||X_i -\xi_i ||_2^2 -\bar{\eta_i } \right)}^2 -\overline{\sigma_i^2 } 
function [F] = getObjective(N, y, eta, eta_bar, sigma)
% returns objective function for sensor network localization problem

F = zeros(N, 1);
F = sym(F);

F(:) = 1 / (4 * sigma^2) * ((y(1, :) - eta(1, 1 : N)).^2 + (y(2, :) - eta(2, 1 : N)).^2) ...
     + 1 / (4 * sigma^2) * ((y(3, :) - eta(1, 2 : end)).^2 + (y(4, :) - eta(2, 2 : end)).^2) ...
     + 1 / (2 * sigma^2) * (sqrt((y(1, :) - y(3, :)).^2 + (y(2, :) - y(4, :)).^2) - eta_bar(:)').^2;

end


function [H] = getInequalityConstr(N, y, eta_bar)
%GETINEQUALITYCONSTR retruns inequality constraint of sensor network
%localization probelm
 H = zeros(N, 1);
 H = sym(H);
 
 H(:) = (sqrt((y(1, :) - y(3, :)).^2 + (y(2, :) - y(4, :)).^2) - eta_bar(:)').^2;

end

IMPLEMENTATION OF THE COUPLING CONSTRAINTS

\zeta_i = \eta_{i+1}
\sum A_i.x_i=0
\begin{array}{l} A_1 =\left\lbrack \begin{array}{cc} 0 & I\\ 0 & 0\\ 0 & 0\\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ 0 & 0\\ -I & 0 \end{array}\right\rbrack ,{\;\;A}_2 =\left\lbrack \begin{array}{cc} -I & 0\\ 0 & I\\ 0 & 0\\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ 0 & 0\\ 0 & 0 \end{array}\right\rbrack ,{\;\;\;A}_3 =\left\lbrack \begin{array}{cc} 0 & 0\\ -I & 0\\ 0 & I\\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ 0 & 0\\ -I & 0 \end{array}\right\rbrack ,\ldotp \ldotp \ldotp \ldotp ,A_N =\left\lbrack \begin{array}{cc} 0 & 0\\ 0 & 0\\ 0 & 0\\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ \ldotp & \ldotp \\ -I & 0\\ 0 & I \end{array}\right\rbrack \\ \\ \mathrm{while}\;\mathrm{setting},\;I=\left\lbrack \begin{array}{cc} 1 & 0\\ 0 & 1 \end{array}\right\rbrack \end{array}

IMPLEMENTATION OF THE COUPLING CONSTRAINTS

function [AA] = getCouplingMatrix(N, n)
% GETCOUPLINGMATRIX returns the coupling matrix of sensor network
% localization problem

I = [1, 0; 0, 1];
A0 = zeros(2*N, n);

A_1 = A0;
A_1(1:2, 3:4) = I;
A_1(2*N - 1: 2*N, 1:2) = -I;

AA(1) = mat2cell(A_1, 2 * N, n);

for i = 2 : 1 : N
    A_i = A0;
    A_i(2*(i-2) + 1 : 2*(i-2) + 2, 1:2) = -I;
    A_i(2*i - 1: 2*i, 3:4 ) = I;
    AA(i) = mat2cell(A_i, 2*N, n);
end

end

THE START VECTOR DEFINITION

function [zz0] = getStartValue(N, sigma)
%GETSTARTVALUE returns a start value for ALADIN opimization

initial_position = zeros(2, N);

for i = 1  : N
    initial_position(1, i) = N * cos( 2 * i * pi / N ) + normrnd(0, sigma);
    initial_position(2, i) = N * sin( 2 * i * pi / N ) + normrnd(0, sigma);
end

 zz0 = cell(1, N);
for i = 1 : N-1
    zz0(i) = {[initial_position(:, i); initial_position(:, i + 1)]};
end
 zz0(N) = {[initial_position(:, N); initial_position(:, 1)]};

end

SETTTING UP AN ALADIN SOLVER

function [sProb ] = setupSolver(N, sigma)

% general setup

n       = 4;   % dimension of design variables          
d       = 2;   % dimension of coordinate system 

% initialization of variables

 y = sym('y%d%d', [N n], 'real');
 y = y';

% get estimated initial positions
 [eta, eta_bar] = getEta(N, d, sigma);

% definition of objective functions
 F = getObjective(N, y, eta, eta_bar, sigma);

% definition of inequality constraint
 H = getInequalityConstr(N, y, eta_bar);
 
% definition of counpling matrices
 AA = getCouplingMatrix(N, n);

% start value for optimization
 zz0 = getStartValue(N, sigma); 



%% setting up solver

% set search area
sProb.llbx = cell(1, N);
sProb.uubx = cell(1, N);
for i = 1 : N
    sProb.llbx(i) = mat2cell([-inf; -inf; -inf; -inf], 4, 1);
    sProb.uubx(i) = mat2cell([ inf;  inf;  inf;  inf], 4, 1);
end

% handover of functions
sProb.locFuns.ffi          = cell(1, N);
sProb.locFuns.hhi          = cell(1, N);


for i = 1 : N
    sProb.locFuns.ffi(i) = {matlabFunction(F(i), 'Vars', {y(:, i)})} ;
    sProb.locFuns.hhi(i) = {matlabFunction(H(i), 'Vars', {y(:, i)})} ;
end


sProb.AA = AA;
sProb.zz0 = zz0;

PERFORMING RUNTIME ANALYSIS FOR COMPARISON

clear all
N = [5, 10, 15 , 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100];
sigma = [0.5, 1, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5];

opts.maxiter = 5;

time = zeros(2, length(N));


for i = 1 : length(N)
    sProb = setupSolver(N(i), sigma(i));
    opts.parfor = 'true'; 

    time_parfor = tic;
    sol = run_ALADIN(sProb, opts);
    time(1, i) = toc(time_parfor);

    time_for = tic;
    opts.parfor = 'false';
    sol = run_ALADIN(sProb, opts);
    time(2, i) = toc(time_for);
end

figure 
plot(N, time(1, :))
title('runtime analysis')
hold on
plot(N, time(2, :))
hold off
legend('time parfor', 'time for')
xlabel('number of sensors')
ylabel('time [s]')

THE OUTPUT OBTAINED AS THE RESULT

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