Artificial neural network

Workings of a network

Cells

A network consists of cells that have either positive or negative connections to other cells

Calculus

Sigmoid function

This is a function that returns values between 0 and 1, and gives around 0.5 when given a zero:

  • Logistic function
  • hyperbolic tangent
  • arctangent function
  • Gudermannian function
  • Error function
  • Generalised logistic function
  • Smoothstep function

Calculus

Sigmoid function - Logistic function

function sigmoid(input) {
	return 1
	    / (1 + Math.pow(Math.E, -input));
}

Calculus

Communications between the cells

// Calculate

const outputCell1 = sigmoid(
    weigthsCell1[0]
    + weigthsCell1[1] * inputs[0]
    + weigthsCell1[2] * inputs[1]
    + weigthsCell1[3] * inputs[2]
);
const outputCell2 = sigmoid(
    weigthsCell2[0]
    + weigthsCell2[1] * inputs[0]
    + weigthsCell2[2] * inputs[1]
    + weigthsCell2[3] * inputs[2]
);
const inputs = [
    1,
    0,
    1,
];

const weigthsCell1 = [
    3,
    5,
    -2,
    -10,
];

const weigthsCell2 = [
    -7,
    -1,
    -4,
    -14,
];

Result

 

Training your network

Training

Training is based on evolution

Every generation either gets better, or stays the same

Training

Evolution can happen in different ways

Depending on the task at hand, the "supervisor" chooses a way of "reproduction"

1 Survivor per generation

The half of the population survives

 

One child allowed

Training

Training itself too

Supervised training

 

 

  • All tasks are known beforehand
  • The task is clear

Semi-supervised training

 

  • Some problems are known, others not
  • Can feed into next layers

Unsupervised training

 

 

  • No input is known
  • When the input data is large

Depending on the task at hand, the "supervisor" chooses a way of "training"

Training

Training itself too

Supervised training

 

Semi-supervised training

Unsupervised training

 

Cons and pros for Neural networks

Pros:

  • Can find new solutions
  • Can learn from unique input

Cons:

Summary

 

Neural network have the following properties:

 

  • Topology
  • Way of "evolving"
  • Way of "training"

Questions?

Tool for neural networks:

Artificial Neural Network

By Fernando van Loenhout

Artificial Neural Network

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