PHP写的求多项式导数的函数代码

　　<?php

　　function getDerivativeByFormulaAndXDATA($formula, $x_data){

　　$xArray = explode("+", $formula);

　　$Derivative = 0;

　　foreach ($xArray as $x_record) {

　　$tmpArray = explode("x^", $x_record);

　　if(count($tmpArray) == 2){

　　$coefficient = $tmpArray[0]==""?1:$tmpArray[0];

　　$exp = $tmpArray[1];

　　}

　　//constant

　　else {

　　$coefficient = $tmpArray[0];

　　$exp = 0;

　　}

　　$Derivative += $coefficient*$exp*pow($x_data,$exp-1);

　　}

　　return $Derivative;

　　}

　　function getValueByFormulaAndXDATA($formula, $x_data){

　　$xArray = explode("+", $formula);

　　$y_data = 0;

　　foreach ($xArray as $x_record) {

　　$tmpArray = explode("x^", $x_record);

　　if(count($tmpArray) == 2){

　　$coefficient = $tmpArray[0]==""?1:$tmpArray[0];

　　$exp = $tmpArray[1];

　　}

　　//constant

　　else {

　　$coefficient = $tmpArray[0];

　　$exp = 0;

　　}

　　$y_data += $coefficient*pow($x_data,$exp);

　　}

　　return $y_data;

　　}

　　function getMaxDerivativeByFormulaAndXDATAS($formula, $x_datas, &$matchs){

　　$derivatives = array();

　　$max_derivative = 0;

　　foreach ($x_datas as $x_data) {

　　$derivative = getDerivativeByFormulaAndXDATA($formula, $x_data);

　　$derivatives[$x_data] = $derivative;

　　$max_derivative = $max_derivative>=abs($derivative)?$max_derivative:abs($derivative);

　　//printf("x=%f, derivative=%f \n",$x_data, $derivative);

　　}

　　$matchs = array();

　　foreach ($derivatives as $x_data=>$derivative) {

　　if(abs($derivative) == $max_derivative){

　　$matchs[] = $x_data;

　　}

　　}

　　printf("max derivative=%f\n",$max_derivative);

　　foreach ($matchs as $x_match) {

　　printf(" derivative=%f when x=%f\n",$derivatives[$x_match], $x_match);

　　}

　　}

　　//notice the format of formula: ax^b if b=0 could omit except coefficient a, if a=1 could omit coefficient

　　$formula = "x^2+2x^1+1";

　　print "The formula is $formula \n";

　　//printf("Derivative of 2 is %f \n",getDerivativeByFormulaAndXDATA($formula, 3.2));

　　//print getValueByFormulaAndXDATA($formula, 3.2)."\n";

　　$sampleData = array(-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,1,2,3,4,5,6,7,8,9,10,11,12);

　　foreach ($sampleData as $x_data) {

　　$str.=$x_data.", ";

　　}

　　print "sample x values: $str \n";

　　getMaxDerivativeByFormulaAndXDATAS($formula, $sampleData, $matchs)."\n";

　　?>