Deep Learning

Notes for CMSC 828W: Foundations of Deep Learning (Fall 2020) taught by Soheil Feizi

• Course Website

My notes are intended to be a concise reference for myself, not a comprehensive replacement for lecture.
I may omit portions covered in other wiki pages or things I find less interesting.

Basics

A refresher of Machine Learning and Supervised Learning.

Empirical risk minimization (ERM)

Minimize loss function over your data: \(\displaystyle \min_{W} \frac{1}{N} \sum_{i=1}^{N} l(f_{W}(x_i), y_i))\)

Loss functions

For regression, can use quadratic loss: \(\displaystyle l(f_W(x), y) = \frac{1}{2}\Vert f_W(x)-y \Vert^2\)

For 2-way classification, can use hinge-loss: \(\displaystyle l(f_W(x), y) = \max(0, 1-yf_W(x))\)

For multi-way classification, can use cross-entropy loss:
\(\displaystyle g(z)=\frac{1}{1+e^{-z}}\)
\(\displaystyle \min_{W} \left[-\sum_{i=1}^{N}\left[y_i\log(y(f_W(x_i)) + (1-y_i)\log(1-g(f_W(x_i))\right] \right]\)

Nonlinear functions

Given an activation function \(\phi()\), \(\phi w^tx + b\) is a nonlinear function.

Models

Multi-layer perceptron (MLP): Fully-connected feed-forward network.

Convolutional neural network