67 lines
1.8 KiB
PHP
67 lines
1.8 KiB
PHP
<?php
|
|
// Statistics/Basic
|
|
basic_stats(100);
|
|
echo PHP_EOL;
|
|
basic_stats(1000);
|
|
echo PHP_EOL;
|
|
basic_stats(10000);
|
|
echo PHP_EOL;
|
|
|
|
function basic_stats (int $sample_size) {
|
|
if ($sample_size < 1) return;
|
|
srand((double)microtime() * 1000000);
|
|
$r = array_fill(0, $sample_size, 0);
|
|
$h = array_fill(0, 10, 0);
|
|
$sum = 0.0;
|
|
$h_sum = 0;
|
|
|
|
// Generate '$sample_size' normally distributed random numbers with $mean 0.5
|
|
// and standard deviation 0.25
|
|
// calculate their $sum
|
|
// and in which box they will fall when drawing the histogram
|
|
for ($i = 0; $i < $sample_size; $i++) {
|
|
$r[$i] = mt_rand() / mt_getrandmax();
|
|
$sum += $r[$i];
|
|
$h[floor($r[$i] * 10)]++;
|
|
}
|
|
|
|
foreach ($h as $h_item)
|
|
$h_sum += $h_item;
|
|
// adjust one of the $h values if necessary to ensure $h_sum = $sample_size
|
|
$adj = $sample_size - $h_sum;
|
|
if ($adj != 0) {
|
|
for ($i = 0; $i < 10; $i++) {
|
|
$h[$i] += $adj;
|
|
if ($h[$i] >= 0) break;
|
|
$h[$i] -= $adj;
|
|
}
|
|
}
|
|
$mean = $sum / $sample_size;
|
|
|
|
$sum = 0.0;
|
|
// Now calculate their standard deviation
|
|
foreach ($r as $r_item)
|
|
$sum += pow($r_item - $mean, 2);
|
|
$sd = sqrt($sum / $sample_size);
|
|
|
|
// Draw a histogram of the data with interval 0.1
|
|
// If sample size > 300 then normalize histogram to 300
|
|
$scale = 1.0;
|
|
if ($sample_size > 500)
|
|
$scale = 500.0 / $sample_size;
|
|
echo 'Sample size '.$sample_size.PHP_EOL;
|
|
echo ' Mean '.
|
|
str_pad(number_format($mean, 6, '.', ''), 8, ' ', STR_PAD_LEFT).
|
|
' SD '.
|
|
str_pad(number_format($sd, 6, '.', ''), 8, ' ', STR_PAD_LEFT).PHP_EOL;
|
|
$i = 0;
|
|
foreach ($h as $h_item) {
|
|
echo ' '.
|
|
str_pad(number_format($i / 10.0, 2, '.', ''), 4, ' ', STR_PAD_LEFT).
|
|
' : ';
|
|
echo str_pad($h_item, 5, ' ', STR_PAD_LEFT).' '.
|
|
str_repeat('*', round($h_item * $scale)).PHP_EOL;
|
|
$i++;
|
|
}
|
|
}
|
|
?>
|