PHP中XOR (异或)训练，很久不看PHP，突然发现已经非常强大了，什么SVM、FANN一应俱全了，谁让AI大潮了

本文介绍如何使用FANN库训练神经网络实现XOR功能。通过定义网络结构及参数，利用特定的数据集进行训练，并演示了如何加载训练好的模型进行测试。

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http://php.net/manual/zh/book.fann.php

以下例子展示了怎么训练数据来实现 XOR (异或)功能。

Example #1 xor.data file

数据解读：

Here is an explanation for the input file for training, as it might be obvious to everyone and you must understand it to write your own:

4 2 1 <- header file saying there are 4 sets to read, with 2 inputs and 1 output
-1 -1 <- the 2 inputs for the 1st group
-1    <- the 1 output for the 1st group
-1 1  <- the 2 inputs for the 2nd group
1     <- the 1 output for the 2nd group
1 -1  <- the 2 inputs for the 3rd group
1     <- the 1 output for the 3rd group
1 1   <- the 2 inputs for the 4th group
-1    <- the 1 output for the 4th group

Example #2 一般训练

<?php
$num_input = 2;
$num_output = 1;
$num_layers = 3;
$num_neurons_hidden = 3;
$desired_error = 0.001;
$max_epochs = 500000;
$epochs_between_reports = 1000;

$ann = fann_create_standard($num_layers, $num_input, $num_neurons_hidden, $num_output);

if ($ann) {
    fann_set_activation_function_hidden($ann, FANN_SIGMOID_SYMMETRIC);
    fann_set_activation_function_output($ann, FANN_SIGMOID_SYMMETRIC);

    $filename = dirname(__FILE__) . "/xor.data";
    if (fann_train_on_file($ann, $filename, $max_epochs, $epochs_between_reports, $desired_error))
        fann_save($ann, dirname(__FILE__) . "/xor_float.net");

    fann_destroy($ann);
}
?>

这个例子展示怎么读取神经网络并且使用 XOR (异或)功能来运行数据。

Example #3 一般测试

<?php
$train_file = (dirname(__FILE__) . "/xor_float.net");
if (!is_file($train_file))
    die("The file xor_float.net has not been created! Please run simple_train.php to generate it");

$ann = fann_create_from_file($train_file);
if (!$ann)
    die("ANN could not be created");

$input = array(-1, 1);
$calc_out = fann_run($ann, $input);
printf("xor test (%f,%f) -> %f\n", $input[0], $input[1], $calc_out[0]);
fann_destroy($ann);
?>

简单的异或问题就搞定了！！！

A helpful reference for FANN is available here:
http://leenissen.dk/fann/html/files2/theory-txt.html