Phpml\NeuralNetwork\Training\Backpropagation::trainSample PHP Method

    private function trainSample(array $sample, array $target)
    {
        $this->network->setInput($sample)->getOutput();
        $this->sigmas = [];
        $layers = $this->network->getLayers();
        $layersNumber = count($layers);
        for ($i = $layersNumber; $i > 1; --$i) {
            foreach ($layers[$i - 1]->getNodes() as $key => $neuron) {
                if ($neuron instanceof Neuron) {
                    $sigma = $this->getSigma($neuron, $target, $key, $i == $layersNumber);
                    foreach ($neuron->getSynapses() as $synapse) {
                        $synapse->changeWeight($this->theta * $sigma * $synapse->getNode()->getOutput());
                    }
                }
            }
        }
    }