Deep Learning in NLP

The Old Way of doing things...

• Bag of words
  • This movie wasn't particularly funny or entertaining -> [movie, funny, entertaining] 
• n-grams(next slide)
• Regex Patterns, etc.

n-grams example

Suggested Reading:

n-grams/naive bayes

• Columbia University: n-grams 
• Naive Bayes in Python

Neural Networks

...Neural Networks

a beautiful, highly flexible and generic biologically-inspired programming paradigm which enables a computer to learn from observational data

Backpropagation

Suggested Reading: 

Neural Networks

• A Neural Network in 11 Lines of Python
• http://neuralnetworksanddeeplearning.com/chap2.html
• Calculus on Computational Graphs
• Convex Optimization Overview

Word Vector Embeddings

Vector Space Models

• Creates a d-dimensional space, where each word is represented by a point in this space
• All the words with a very high co-occurrence will be clustered together
• Understands semantic relations between words
• Each dimension explains one of the characteristics of the natural language like plural, past tense, opposite gender, etc.

Introduction to Gensim

• A Python based library that provides modules for word2vec, LDA, doc2vec, etc.
• Options for training word vectors using skip gram and CBOW
• In built scripts to train word vectors over wikipedia dumps

...Gensim

model = Word2Vec(sentences, size=100, window=5, min_count=5, workers=4)

model.save(fname)
model = Word2Vec.load(fname)  # you can continue training with the loaded model!

model.most_similar(positive=['woman', 'king'], negative=['man'])
==> [('queen', 0.50882536), ...]

model.doesnt_match("breakfast cereal dinner lunch".split())
==> 'cereal'

model.similarity('woman', 'man')
==> 0.73723527

model['computer']  # raw numpy vector of a word
==> array([-0.00449447, -0.00310097,  0.02421786, ...], dtype=float32)

...Gensim

Suggested Reading:

Word Vectors

• From Frequency to Vector: Vector Space model of semantics
• Compositionality and Distributed Representations 
• Efficient Estimation of Word Representations in Vector Space
• Glove Vectors

Introduction to Theano

Theano is a Python library that allows you to define, optimize, and evaluate mathematical expressions involving multi-dimensional arrays efficiently.

• Built on top of numpy
• Symbolic Expressions
• Automatic Differentiation
• In built integration for GPU Computation
• Python Interface
• Shared Variables

Theano Syntax

import numpy
import theano
import theano.tensor as T
from theano import pp

x = T.dscalar('x')
y = x ** 2
gy = T.grad(y, x)
f = theano.function([x], gy)
f(4)
# array(8.0)

Suggested Reading:

Theano

• DeepLearning.net Theano Tutorial
• Speading up your neural network with Theano

Deep Neural Networks

Suggested Reading:

Deep Learning Models

• Regularization and Activation Functions in Neural Nets
• Learning Deep Architectures
• Deep Learning with Neural Networks
• Deep Learning - An MIT Press Book
• Practical recommendations for gradient-based training of deep architectures

Recurrent Neural Networks

...RNNs

• particularly useful for sequential data(text, audio, etc.)
• "Recurrent" because they performs the same operations on each element of the input
• considers the dependencies between the input elements(words), contrary to bag-of-words model
• common RNNs are 5-1000 layer deep

Language Modelling

Probability of a sentence consisting of 'm' words

= 

Multiplication of Joint probability of each word conditioned upon (all) previous words

LM with RNN

Back Propagation in Time

Vanishing Gradient Problem

Long-Short Term Memory

LSTM Eqns