<?
# Second version of deriv
# Tread with caution
class deriv {
var $ds = array(
'log(ax+b)' => 'd(ax+b)/(ax+b)',
'cos(ax+b)' => '-1*sin(ax+b)*d(ax+b)',
'sin(ax+b)' => '1*cos(ax+b)*d(ax+b)');
function derivate_poly($function) {
// Hybrid.
// Function format: k(poly)^n + k(poly)^n etc...
// k and n integers
$q = explode(" ",$function);
foreach ($q as $r => $s) {
if (strlen($s) > 1) {
$t = eregi("([0-9]+)\((.+)\)\^([0-9-])",$s,$w);
if (is_array($w)) {
if ($w[3] == 1) {
$c1 = $w[1];
$c2 = $this->derivate_single(str_replace("+"," + ",str_replace("-"," - ",$w[2])));
$df[] = $c1*$c2."x^0";
}
elseif ($w[3] == 0) $df[] = 0;
else {
$c1 = $w[1]*$w[3];
$pfin = $w[3]-1;
$c2 = $this->derivate_single(str_replace("+"," + ",str_replace("-"," - ",$w[2])));
if (is_int($c2)) {
$c3 = $c1*$c2;
$df[] = $c3."(".$w[2].")^".$pfin;
}
else {
$df[] = $c1."(".$c2.")(".$w[2].")^".$pfin;
}
}
}
else $df[] = $s;
}
else $df[] = $t;
}
return implode($df);
}
function derivate_single($function) {
// Fastest function for a straight polynomic
// Format: kx^n + kx^n + kx^n
// k and n integers. If no x, n=0
$a = explode(" ",$function);
foreach ($a as $b => $c) {
if (strlen($c) > 1) {
$r = eregi("([0-9]+)x\^([0-9-]+)",$c,$d);
if (is_array($d)) {
if ($d[2] > 1 or $d[2] < -1) $deriv[] = ($d[1]*$d[2])."x^".($d[2]-1);
elseif (abs($d[2]) == 1) $deriv[] = $d[1];
else array_pop($deriv);
unset($d);
}
else $deriv[] = $c;
}
else $deriv[] = $c;
}
return implode(" ",$deriv);
}
}
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