Deep Reinforcement Learning
Supervised learning has a fixed dataset. Reinforcement learning creates its own, which changes everything.
Supervised learning has a fixed dataset. Reinforcement learning creates its own, which changes everything.
The model is the easy part. Everything after training is where deployments fail.
A change too small to see can flip a classifier’s answer. That is a property of the models, not a bug in one of them.
A softmax output of 0.99 is not a 99% chance of being right. Here is how far apart those two things are.
A model that is right for the wrong reason will fail the moment the reason changes.
Images have a grid, sentences have an order, and a molecule has neither. Message passing is the generalization.
Labels are the expensive part of supervised learning. These methods construct the supervision from the data itself.
Reconstruction is a pretext. What you actually want is the code in the middle.
A transformer sees an image as a sequence of patches and assumes nothing about geometry. That is both its strength and its data requirement.
Every component explained separately, now assembled into something you can train tonight.
Every model’s view of language is filtered through its tokenizer, and most surprising model behavior starts there.
Remove recurrence, keep attention, and add back the position information you just threw away.
Attention was invented to fix one specific failure: compressing a whole sentence into one vector.
Gates exist for one reason: to give the gradient an additive path through time.
A word’s meaning is approximated by the company it keeps. That single idea produces vectors you can do arithmetic on.
The one task where you freeze the network and train the image instead.
When every person is a class and new people arrive daily, classification stops being the right formulation.
Classification per pixel sounds simple until you have to recover the resolution you threw away.
Detection is classification plus regression plus a deduplication problem nobody mentions until it breaks.
Almost nobody trains an image classifier from scratch. Here is what the alternative actually looks like.
Each architecture solved one specific problem left over from the previous one.
A convolution is a fully connected layer with two constraints. Those constraints are the whole idea.
When training data and production data differ, the usual bias-variance diagnosis gives the wrong answer.
The hard part is not training a model. It is knowing which of ten possible improvements to try next.
Multiple GPUs are not free speed. Here is what actually has to be synchronized.
Most training loops are slower than they need to be, and the bottleneck is rarely where people assume.
An experiment you cannot repeat is an anecdote, not a result.
Six lines in the right order, and the reasons each one has to be there.
Autograd is the computation graph you already built, constructed for you at runtime.
Tuning is a search problem with a budget. Spend it on the parameters that matter.
A practical framework for recognizing overfitting and choosing the right regularization method.
Every normalization layer answers the same question differently: which axes do we average over?
The learning rate is the single most important hyperparameter, and a constant value is almost never the right choice.
Understand what popular deep-learning optimizers remember, how they update parameters, and when to tune the learning rate.
A wrong gradient produces a model that trains slowly instead of crashing. Here is how to catch it.
Initialization is not a detail. It decides whether a deep network trains at all.
The loss function is the only place where you tell a network what “better” means. Choose it deliberately.
Extend binary logistic regression to many classes with softmax, cross-entropy, and a numerically stable NumPy implementation.
Follow data and gradients through an L-layer neural network with dimension rules and reusable NumPy formulas.
Implement a one-hidden-layer neural network from scratch and understand every forward and backward equation.
A visual and numerical explanation of how local derivatives combine into backpropagation through a computation graph.
A beginner-friendly explanation of neural-network structure, notation, hidden layers, and forward propagation with a verified NumPy example.
A practical guide to logistic regression, from probability and cross-entropy to vectorized gradients and a complete NumPy implementation.
Replace slow loops with clear matrix operations and learn how to prevent silent broadcasting and shape errors in NumPy.
Every loss function in this series is a probability statement in disguise. Here is the vocabulary.
A neural network is a stack of matrix multiplications. This is the algebra that makes that sentence mean something.