How it looks in pure PHP
A minimal one-neuron backpropagation example in PHP
A minimal example of a single neuron. Everything we just computed by hand is now written as code. There is no extra logic in the program – the same formulas are simply expressed in PHP.
Example of code:
<?php
function sigmoid($x) {
return 1 / (1 + exp(-$x));
}
// σ'(z)=σ(z)(1−σ(z)), so the already computed activation suffices
// therefore, recomputing sigmoid(z) is not required
function sigmoid_derivative($a) {
return $a * (1 - $a);
}