PHP: Математические функции - Manual

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Last updated: Fri, 26 Jan 2007

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# LXXVIII. Математические функции

# Введение

Данные функции работают с числами в диапазонах типов integer и float на вашей машине (это отвечает C-типам long и double). Если вам нужно работать с большими числами, обратитесь к разделу Ссылка VII, BCMath Arbitrary Precision Mathematics Functions.

См. также Разд. Арифметические операторы в Гл. 15.

# Требования

Эти функции всегда доступны.

# Установка

Для использования этих функций не требуется проведение установки, поскольку они являются частью ядра PHP.

# Настройка во время выполнения

Данное расширение не определяет никакие директивы конфигурации в `php.ini`.

# Типы ресурсов

Данное расширение не определяет никакие типы ресурсов.

# Предопределенные константы

Перечисленные ниже константы всегда доступны как часть ядра PHP.

Таблица 1. Математические константы

Константа | Значение | Описание
--- | --- | ---
M_PI | 3.14159265358979323846 | число пи
M_E | 2.7182818284590452354 | число Эйлера
M_LOG2E | 1.4426950408889634074 | log_2 e
M_LOG10E | 0.43429448190325182765 | lg e
M_LN2 | 0.69314718055994530942 | ln 2
M_LN10 | 2.30258509299404568402 | ln 10
M_PI_2 | 1.57079632679489661923 | пи/2
M_PI_4 | 0.78539816339744830962 | пи/4
M_1_PI | 0.31830988618379067154 | 1/пи
M_2_PI | 0.63661977236758134308 | 2/пи
M_SQRTPI | 1.77245385090551602729 | sqrt(пи) [4.0.2]
M_2_SQRTPI | 1.12837916709551257390 | 2/sqrt(пи)
M_SQRT2 | 1.41421356237309504880 | sqrt(2)
M_SQRT3 | 1.73205080756887729352 | sqrt(3) [4.0.2]
M_SQRT1_2 | 0.70710678118654752440 | 1/sqrt(2)
M_LNPI | 1.14472988584940017414 | ln пи [4.0.2]
M_EULER | 0.57721566490153286061 | Постоянная эйлера [4.0.2]

В версиях PHP до 4.0.0 включительно доступна только M_PI. Все остальные были добавлены с следующей версии, кроме констант с пометкой [4.0.2], которые были добавлены в версии PHP 4.0.2.
add a note User Contributed Notes
Математические функции
barry at megaspace dot com
02-Dec-2006 09:14
`Here's a least common denominator (lcd) function:
$array = array(3,4,6,8,18,2);
function lcd($array,$x) {
$mod_sum = 0;
for($int=1;$int < count($array);$int++) {
$modulus[$int] = ($array[0]*$x) % ($array[$int]);
$mod_sum = $mod_sum + $modulus[$int];
}
if (!$mod_sum) {
echo "LCD: ".($array[0]*$x)."\n";
}
else {
lcd($array,$x+1);
}
}
lcd($array,1);`
tembenite at gmail dot com
06-Nov-2006 01:36
`To add to what Cornelius had, I have written a function that will take an array of numbers and return the least common multiple of them:
function lcm_arr($items){
//Input: An Array of numbers
//Output: The LCM of the numbers
while(2 <= count($items)){
array_push($items, lcm(array_shift($items), array_shift($items)));
}
return reset($items);
}
//His Code below with $'s added for vars
function gcd($n, $m) {
$n=abs($n); $m=abs($m);
if ($n==0 and $m==0)
return 1; //avoid infinite recursion
if ($n==$m and $n>=1)
return $n;
return $m<$n?gcd($n-$m,$n):gcd($n,$m-$n);
}
function lcm($n, $m) {
return $m * ($n/gcd($n,$m));
}`
tim at durge dot org
27-Oct-2006 05:51
`In Evan's ordinal function, the line:
<?php
$tens = substr($cardinal, -2, 1);
?>
needs to be replaced by:
<?php
$tens = round($cardinal/10);
?>
or similar. At least on PHP 4.3.10, substr("1", -2, 1) returns '1' - so Evan's function gives "1th", as well as "11th". This is contrary to the documentation, but is noted in the comments on the substr manual page.`
Evan Broder
26-Jul-2006 11:42
`A slightly more complex but much more accurate cardinal=>ordinal function (the one below doesn't account for 11th, 12th, and 13th, which don't follow the usual rules):
<?php
function ordinal($cardinal)
{
$cardinal = (int)$cardinal;
$digit = substr($cardinal, -1, 1);
$tens = substr($cardinal, -2, 1);
if($tens == 1)
{
return $cardinal.'th';
}
switch($digit)
{
case 1:
return $cardinal.'st';
case 2:
return $cardinal.'nd';
case 3:
return $cardinal.'rd';
default:
return $cardinal.'th';
}
}
?>`
g8z at yahoo dot com
19-Jul-2006 11:15
`<?php
/**
generate_ratio outputs the properly reduced ratio of the two numbers specified. This function is divide by zero safe.
Courtesy of the $5 Script Archive: http://www.tufat.com
**/
function generate_ratio($number_1, $number_2)
{
// figure out which number is lowest
$lowest = $number_1;
if ($number_2 < $lowest)
$lowest = $number_2;
// find the greatest common factor
$gcf = 1;
for ($count=$lowest + 1; $count >= 1; $count--) {
if (($number_1 % $count == 0 && $number_2 % $count == 0) && $count > $gcf)
$gcf = $count;
}
// reduce
$number_1 /= $gcf;
$number_2 /= $gcf;
// return ratio string
$ratio = $number_1 . ':' . $number_2;
return $ratio;
}
// EXAMPLE:
print generate_ratio(44, 32);
?>`
edward at edwardsun dot com
19-Jul-2006 06:24
`well just a note.. maybe i'm a bit stupid.. but remember to use pow() rather than the "^" sign for exponents.. as it took me 5 minutes to figure out why it wasn't working.`
jaakko dot mantila at sagas dot fi
12-Jul-2006 03:10
`Here is another payment function with working future value($fv) option:
function payment($r,$np,$pv,$fv,$prec) {
/* Calculates the monthly payment
** $apr = the annual percentage rate of the loan.
** $n = number of monthly payments (360 for a 30year loan)
** $pv = present value or principal of the loan
** $fv = future value of the loan (after payments)
** $prec = the precision you wish rounded to
*/
/****************************************\
** No Warranty is expressed or implied. **
*****************************************/
if(!$fv) $fv = 0;
$mypmt=$r * (-$fv+pow((1+$r),$np)*$pv)/(-1+pow((1+$r),$np));
return round($mypmt, $prec);
}`
twoscoopsofpig at NOSPAM dot gmail dot com
07-Jul-2006 09:07
`@ Moikboy:
This may or may not be more simplified factorialization:
<?php
$f=$fact=25;
while ($fact>0)
{$f=$f*$fact--;}
echo $f;
?>`
marasek.SPAMLESS at telton.de
08-Jun-2006 05:23
`I could not resist to do a simpler version of the ordinal function:
<?php
function ordinal($num)
{
$num = (int)$num;
$digit = substr($num, -1, 1);
$ord = "th";
switch($digit)
{
case 1: $ord = "st"; break;
case 2: $ord = "nd"; break;
case 3: $ord = "rd"; break;
break;
}
return $num.$ord;
}
?>
One could replace the typecast with
<?php
if($num===NULL or $num==="")
{return NULL;}
?>
to get an empty result instead of "0th" in case $num is empty too.`
moikboy (nospam!) moikboy (nospam!) hu
10-May-2006 01:15
`I think, this is the optimal code for calculating factorials:
<?php
function fact($int){
if($int<2)return 1;
for($f=2;$int-1>1;$f*=$int--);
return $f;
};
?>
And another one for calculating the $int-th Fibonacci-number:
<?php
function fib($int){
static $fibTable=array();
return empty($fibTable[$int])?$fibTable[$int] = $int>1?fib($int-2)+fib($int-1):1:$fibTable[$int];
};
?>`
nessthehero at comcast dot net
21-Mar-2006 02:48
`Just a simple function to find the ordinal ending to any number if you're printing for example: "The nth result is..."
function ordinal($num) {
$digit = substr($num,-1,1);
$ord = array(
0 => 'th',
1 => 'st',
2 => 'nd',
3 => 'rd',
4 => 'th',
5 => 'th',
6 => 'th',
7 => 'th',
8 => 'th',
9 => 'th'
);
$string = $num.$ord[$digit];
return $string;
}`
Florian
03-Mar-2006 01:36
`A function that simulates the sum operator. (http://en.wikipedia.org/wiki/Sum). Be careful with the expression because it may cause a security hole; note the single quotes to don't parse the "$".
<?php
# @param string $expr expression to evaluate (for example (2*$x)^2+1)
# @param string $var dummy variable (for example "x")
# @param integer $start
# @param integer $end
# @param integer $step
function sum($expr,$var,$start,$end,$step = 1) {
$expr = str_replace(';','',$expr);
$var = str_replace('$','',$var);
$start = (int)$start; $end = (int)$end; $step = (int)$step; $sum = 0;
for ($i = $start; $i <= $end; $i = $i + $step) {
$_expr = str_replace('$'.$var,$i,$expr);
$_eval = '$_result = '.$_expr.'; return $_result;';
$_result = eval($_eval);
if($result === FALSE) return "SYNTAX ERROR : $expr";
$sum += $_result;
}
return (int)$sum;
}
?>`
jos at gtacrime dot nl
17-Feb-2006 01:39
`Thanks to Chronial "at" cyberpunkuniverse.de, I was able to create the binompdf(n, p, k) function.
<?php
function nCr($n, $k){
if ($k > $n)
return NaN;
if (($n - $k) < $k)
return nCr($n, ($n - $k));
$return = 1;
for ($i=0; $i<$k; $i++){
$return *= ($n - $i) / ($i + 1);
}
return $return;
}
function binompdf($n, $p, $k){
$return = nCr($n, $k) * pow($p, $k) * pow((1 - $p), ($n - $k));
return $return;
}
?>`
peter-stangl at t-online dot de
01-Feb-2006 03:16
`I needed to approximate an integral because i was not able to calculate it, so i wrote this function. It approximates an integral with the composite Simpson's rule.
More information on Simpson's rule: http://en.wikipedia.org/wiki/Simpson%27s_rule
<?php
function simpsonf($x){
// returns f(x) for integral approximation with composite Simpson's rule
return(pow((1+pow($x, (-4))), 0.5));
}
function simpsonsrule($a, $b, $n){
// approximates integral_a_b f(x) dx with composite Simpson's rule with $n intervals
// $n has to be an even number
// f(x) is defined in "function simpsonf($x)"
if($n%2==0){
$h=($b-$a)/$n;
$S=simpsonf($a)+simpsonf($b);
$i=1;
while($i <= ($n-1)){
$xi=$a+$h*$i;
if($i%2==0){
$S=$S+2*simpsonf($xi);
}
else{
$S=$S+4*simpsonf($xi);
}
$i++;
}
return($h/3*$S);
}
else{
return('$n has to be an even number');
}
}
?>`
daniel at g-loc dot org
01-Dec-2005 10:01
`If you�re an aviator and needs to calculate windcorrection angles and groundspeed (e.g. during flightplanning) this can be very useful.
$windcorrection = rad2deg(asin((($windspeed * (sin(deg2rad($tt - ($winddirection-180))))/$tas))));
$groundspeed = $tas*cos(deg2rad($windcorrection)) + $windspeed*cos(deg2rad($tt-($winddirection-180)));
You can probably write these lines more beautiful, but they work!`
nbraczek at bsds dot de
26-Oct-2005 02:27
`Under some circumstances, it is appropriate to round floats to a given number of significant digits. This function will do it for you:
/**
* Round to significant digits
*
* @param float $f The number to be rounded
* @param integer $n Number of significant digits
*/
function round_significant($f, $n)
{
if ($f==0) return $f;
return round($f, $n-floor(log10(abs($f)))-1);
}`
monte at ohrt dot com
18-Oct-2005 06:37
`This is an efficient method of calculating the binomial coefficient C(n,k). This code was derived from Owant: Mastering Algorithms with Perl.
<?php
// calculate binomial coefficient
function binomial_coeff($n, $k) {
$j = $res = 1;
if($k < 0 || $k > $n)
return 0;
if(($n - $k) < $k)
$k = $n - $k;
while($j <= $k) {
$res *= $n--;
$res /= $j++;
}
return $res;
}
?>
If you compiled php with --enable-bcmath, you can get full integer values of extremely large numbers by replacing:
$res *= $n--;
$res /= $j++;
with:
$res = bcmul($res, $n--);
$res = bcdiv($res, $j++);`
crescentfreshpot at yahoo dot com
26-Jul-2005 07:50
`Median:
number median ( number arg1, number arg2 [, number ...] )
number median ( array numbers )
<?php
function median()
{
$args = func_get_args();
switch(func_num_args())
{
case 0:
trigger_error('median() requires at least one parameter',E_USER_WARNING);
return false;
break;
case 1:
$args = array_pop($args);
// fallthrough
default:
if(!is_array($args)) {
trigger_error('median() requires a list of numbers to operate on or an array of numbers',E_USER_NOTICE);
return false;
}
sort($args);
$n = count($args);
$h = intval($n / 2);
if($n % 2 == 0) {
$median = ($args[$h] + $args[$h-1]) / 2;
} else {
$median = $args[$h];
}
break;
}
return $median;
}
?>`
bjcffnet at gmail dot com
26-Jul-2005 04:57
`thearbitcouncil at gmail dot com, you could just use array_sum():
<?php
function average($arr)
{
if (!is_array($arr)) return false;
return array_sum($arr)/count($arr);
}
$array = array(5, 10, 15);
echo average($array); // 10
?>`
graywh at gmail DELETE dot com
01-Jun-2005 12:48
`If you're really concerned about speed, you could compute the factorial of large numbers using the Gamma function of n-1.
Integral y^(t-1)*Exp(-y) for y from 0 to Infinity
For Fibonacci numbers, there's a better-than-recursive way.
((1+sqrt(5))/2)^(n/sqrt(5)) - ((1-sqrt(5))/2)^(n/sqrt(5))`
eric at woolhiser dot com
10-Mar-2005 08:41
`For all you guys writing mortgage calculators out there:
<?php
function payment($apr,$n,$pv,$fv=0.0,$prec=2){
/* Calculates the monthly payment rouned to the nearest penny
** $apr = the annual percentage rate of the loan.
** $n = number of monthly payments (360 for a 30year loan)
** $pv = present value or principal of the loan
** $fv = future value of the loan
** $prec = the precision you wish rounded to
*/
/****************************************\
** No Warranty is expressed or implied. **
*****************************************/
if ($apr !=0) {
$alpha = 1/(1+$apr/12);
$retval = round($pv * (1 - $alpha) / $alpha /
(1 - pow($alpha,$n)),$prec) ;
} else {
$retval = round($pv / $n, $prec);
}
return($retval);
}
?>`
tmpa at yahoo dot com
19-Feb-2005 12:42
`while joogat's one line function is short, it is probably better to calculate factorial iteratively instead of recursively. keep in mind if you want large factorials, you'll need to use some sort of arbitrary precision integer or perhaps the BCMath functions. then again, unless you're trying to do large numbers (170! is the highest that you can do that does not return infinity) you probably won't notice any time difference.
<?php
function factorial($in) {
// 0! = 1! = 1
$out = 1;
// Only if $in is >= 2
for ($i = 2; $i <= $in; $i++) {
$out *= $i;
}
return $out;
}
?>`
thearbitcouncil at gmail dot com
06-Jan-2005 02:32
`Two functions I didn't find elsewhere... one to compute mean of an array of numbers, and another to computer variance of a sample of numbers. Both take an array of numbers as arguments. Not much error checking, or optimization...
(note: variance function uses the average function...)
<?php
function average($arr)
{
if (!count($arr)) return 0;
$sum = 0;
for ($i = 0; $i < count($arr); $i++)
{
$sum += $arr[$i];
}
return $sum / count($arr);
}
function variance($arr)
{
if (!count($arr)) return 0;
$mean = average($arr);
$sos = 0; // Sum of squares
for ($i = 0; $i < count($arr); $i++)
{
$sos += ($arr[$i] - $mean) * ($arr[$i] - $mean);
}
return $sos / (count($arr)-1); // denominator = n-1; i.e. estimating based on sample
// n-1 is also what MS Excel takes by default in the
// VAR function
}
echo variance(array(4,6,23,15,18)); // echoes 64.7...correct value :)
?>`
info at gavinvincent dot co dot uk
17-Nov-2004 04:34
`If you need to deal with polar co-ordinates for somereason you will need to convert to and from x,y for input and output in most situations: here are some functions to convert cartesian to polar and polar to cartesian
<?
//returns array of r, theta in the range of 0-2*pi (in radians)
function rect2polar($x,$y)
{
if(is_numeric($x)&&is_numeric($y))
{
$r=sqrt(pow($x,2)+pow($y,2));
if($x==0)
{
if($y>0) $theta=pi()/2;
else $theta=3*pi()/2;
}
else if($x<0) $theta=atan($y/$x)+pi();
else if($y<0) $theta=atan($y/$x)+2*pi();
else $theta=atan($y/$x);
$polar=array("r"=>$r,"theta"=>$theta);
return $polar;
}
else return false;
}
//r must be in radians, returns array of x,y
function polar2rect($r,$theta)
{
if(is_numeric($r)&&is_numeric($theta))
{
$x=$r*cos($theta);
$y=$r*sin($theta);
$rect=array("x"=>$x,"y"=>$y);
}
else
{
return false;
}
}
?>`
help at gjbdesign dot com
25-Sep-2004 09:05
`Occasionally a user must enter a number in a form. This function converts fractions to decimals and leaves decimals untouched. Of course, you may wish to round the final output, but that is not included here.
<?php
/*Some example values of $q
$q = "2.5";
$q = "2 1/2";
$q = "5/2";
*/
function Deci_Con($q){
//check for a space, signifying a whole number with a fraction
if(strstr($q, ' ')){
$wa = strrev($q);
$wb = strrev(strstr($wa, ' '));
$whole = true;//this is a whole number
}
//now check the fraction part
if(strstr($q, '/')){
if($whole==true){//if whole number, then remove the whole number and space from the calculations
$q = strstr($q, ' ');
}
$b = str_replace("/","",strstr($q, '/'));//this is the divisor
//isolate the numerator
$c = strrev($q);
$d = strstr($c, '/');
$e = strrev($d);
$a = str_replace("/","",$e);//the pre-final numerator
if($whole==true){//add the whole number to the calculations
$a = $a+($wb*$b);//new numerator is whole number multiplied by denominator plus original numerator
}
$q = $a/$b;//this is now your decimal
return $q;
}else{
return $q;//not a fraction, just return the decimal
}
}?>`
donnieb819 at hotmail dot NOSPAM dot com
16-Sep-2004 05:58
`Method to convert an arbitrary decimal number to its most reduced fraction form (so a string is returned, this method would probably be used for output formatting purposes.) There were other methods similar to this one on the page, but none did quite what I wanted. It's maybe not the most elegant code, but it gets the job done. Hope this helps someone. An iterative form of Euclid's algorithm is used to find the GCD.
<?php
function dec2frac( $decimal )
{
$decimal = (string)$decimal;
$num = '';
$den = 1;
$dec = false;
// find least reduced fractional form of number
for( $i = 0, $ix = strlen( $decimal ); $i < $ix; $i++ )
{
// build the denominator as we 'shift' the decimal to the right
if( $dec ) $den *= 10;
// find the decimal place/ build the numberator
if( $decimal{$i} == '.' ) $dec = true;
else $num .= $decimal{$i};
}
$num = (int)$num;
// whole number, just return it
if( $den == 1 ) return $num;
$num2 = $num;
$den2 = $den;
$rem = 1;
// Euclid's Algorithm (to find the gcd)
while( $num2 % $den2 ) {
$rem = $num2 % $den2;
$num2 = $den2;
$den2 = $rem;
}
if( $den2 != $den ) $rem = $den2;
// now $rem holds the gcd of the numerator and denominator of our fraction
return ($num / $rem ) . "/" . ($den / $rem);
}
?>
Examples:
echo dec2frac( 10 );
echo dec2frac( .5 );
echo dec2frac( 5.25 );
echo dec2frac( .333333333 );
yields:
10
1/2
21/4
333333333/1000000000`
pat.mat AT sympatico DOT com
08-Jun-2004 07:36
`For people interest in Differential Equations, I've done a function that receive a string like: x^2+x^3 and put it in
2x+3x^2 witch is the differantial of the previous equation.
In the code there is one thing missing: the $string{$i} is often going outOfBound (Uninitialized string offset: 6 in...)
if your error setting is set a little too high... I just dont know how to fix this.
So there is the code for differential equation with (+ and -) only:
<?
function differentiel($equa)
{
$equa = strtolower($equa);
echo "Equation de depart: ".$equa."<br>";
$final = "";
for($i = 0; $i < strlen($equa); $i++)
{
//Make a new string from the receive $equa
if($equa{$i} == "x" && $equa{$i+1} == "^")
{
$final .= $equa{$i+2};
$final .= "x^";
$final .= $equa{$i+2}-1;
}
elseif($equa{$i} == "+" || $equa{$i} == "-")
{
$final .= $equa{$i};
}
elseif(is_numeric($equa{$i}) && $i == 0)
{
//gerer parenthese et autre terme generaux + gerer ^apres: 2^2
$final .= $equa{$i}."*";
}
elseif(is_numeric($equa{$i}) && $i > 0 && $equa{$i-1} != "^")
{
//gerer ^apres: 2^2
$final .= $equa{$i}."*";
}
elseif($equa{$i} == "^")
{
continue;
}
elseif(is_numeric($equa{$i}) && $equa{$i-1} == "^")
{
continue;
}
else
{
if($equa{$i} == "x")
{
$final .= 1;
}
else
{
$final .= $equa{$i};
}
}
}
//
//Manage multiplication add in the previous string $final
//
$finalMul = "";
for($i = 0; $i < strlen($final); $i++)
{
if(is_numeric($final{$i}) && $final{$i+1} == "*" && is_numeric($final{$i+2}))
{
$finalMul .= $final{$i}*$final{$i+2};
}
elseif($final{$i} == "*")
{
continue;
}
elseif(is_numeric($final{$i}) && $final{$i+1} != "*" && $final{$i-1} == "*")
{
continue;
}
else
{
$finalMul .= $final{$i};
}
}
echo "equa final: ".$finalMul;
}
?>
I know this is not optimal but i've done this quick :)
If you guys have any comment just email me.
I also want to do this fonction In C to add to phpCore maybe soon...
Patoff`
moc.erawtfostym@evad
26-May-2004 07:04
`The fastest O(1) factorial function has a lookup table of all the factorials that fit within the output range. With an array of the first 34 (float) or 170 (double) factorials, you get identical results in a fraction of the time.`
churkl at hotmail dot com
26-May-2004 01:32
`Here is my factorial function which i think is very simple and without any confusion. email me comments if you like if i had something wrong.
<?php
function factorial($number)
{
$temp = 1;
while ($number > 1){
$temp *= $number--;
}
return $temp;
}
?>`
ausvald at tut dot by
30-Apr-2004 05:48
`I see there are some factorial functions below.
I'll provide the best one:
<?
function factorial($n){ $n=(int)$n;
$f=1;
for(;$n>0;--$n) $f*=$n;
return $f;
}
?>`
florian at shellfire dot de
28-Apr-2004 02:48
`Please note that shorter is not always better
(meaning that really short faculty implementation above).
In my opinion, a clearer way to code this is, including a check
for negative or non-integer values.
In order to calculate the faculty of a positive integer,
an iterative way (which might be harder to understand)
is usually a bit faster, but I am using it only for small
values so it is not really important to me:
<?php
// Calculate the Faculty of a positive int-value
function iFaculty($a_iFac)
{
if ($a_iFac > 0)
{
return $a_iFac * $this->iFaculty($a_iFac - 1);
}
elseif ($a_iFac == 0)
{
return 1;
}
else
{
return 0; // Wrong argument!
}
}
?>
I've also written another function to calculate the
binomial coefficient of 2 values, I didn't find it anywhere yet so I hope it might help someone (works fine with the above stated faculty-function and ready to be used inside of your own classes!)
<?php
// calculates the binomial coefficient "n over k" of 2 positive int values
// f�r n >= k
function iBinCoeff($a_iN, $a_iK)
{
// the binomial coefficient is defined as n! / [ (n-k)! * k! ]
return $this->iFaculty($a_iN) / ($this->iFaculty($a_iN - $a_iK) * $this->iFaculty($a_iK));
}
?>`
Chronial "at" cyberpunkuniverse.de
13-Jan-2004 01:47
`Here are are a nPr and a nPc function
(had to define NaN - don't know, how to this the "rigth" way)
<?php
define (NaN,acos(1.01));
function nCr($n,$r){
if ($r > $n)
return NaN;
if (($n-$r) < $r)
return nCr($n,($n-$r));
$return = 1;
for ($i=0;$i < $r;$i++){
$return *= ($n-$i)/($i+1);
}
return $return;
}
function nPr($n,$r){
if ($r > $n)
return NaN;
if ($r)
return $n*(nPr($n-1,$r-1));
else
return 1;
}
?>`
chris at free-source dot com
07-Oct-2003 09:37
`to "convert" scientific notation to a float simply cast it:
<?php
$val = '3.5e4';
$val = (float) $val;
echo $val;
?>
output:
35000`
jl85 at yahoo dot com
05-Oct-2003 04:00
`Here's yet another greatest common denominator (gcd) function, a reeeeally small one.
function gcd($n,$m){
if(!$m)return$n;return gcd($m,$n%$m);
}
It works by recursion. Not really sure about it's speed, but it's really small! This won't work on floating point numbers accurately though. If you want a floating point one, you need to have at least PHP 4, and the code would be
function gcd($n,$m){
if(!$m)return$n;return gcd($m,fmod($n,$m));
}`
fabien_mornand at yahoo dot fr
30-Sep-2003 03:46
`here is an algorithm to calculate gcd of a number. This is Euclid algorithm i was studying in Maths. I've converted it in php for the fun.
<?php
if($a && $b)
{ $ax=$a; $bx=$b;
$r=fmod($a,$b);
if(!$r){$rx=$r;}
while($r){
$rx=$r;
$a=$b;
$b=$r;
$r=fmod($a,$b);
}
}
echo 'PGCD ('.$ax.' , '.$bx.' ) = '.$rx;
?>`
jordanolsommer at imap dot cc
27-Aug-2003 08:07
`The reason the bitwise AND ("&") operator works to determine whether a number is odd or even is because odd numbers expressed in binary always have the rightmost (2^0) bit = 1 and even numbers always have the 2^0 bit = 0.
So if you do a " 1 & $num", it will return zero if the number is even (since xxxxxxx0 [the even number in binary] and 00000001 [the 1]) don't share any bits, and will return 1 if the number is odd (xxxxxx1 and 000001).
a clever way of doing things, but $num % 2 would work as well i think :).`
matthew_gaddis at yahoo dot com
24-Apr-2003 02:23
`Here is a cleaner factorial function:
function factorial($s){
if($s) $r = $s * factorial($s - 1);
else $r = 1;
return $r;
}`
jerry dot wilborn at fast dot net
16-Apr-2003 11:10
`Here is how to calculate standard deviation in PHP where $samples is an array of incrementing numeric keys and the values are your samples:
$sample_count = count($samples);
for ($current_sample = 0; $sample_count > $current_sample; ++$current_sample) $sample_square[$current_sample] = pow($samples[$current_sample], 2);
$standard_deviation = sqrt(array_sum($sample_square) / $sample_count - pow((array_sum($samples) / $sample_count), 2));`
jl85 at yahoo dot com
22-Feb-2003 08:04
`Theres another faster way of doing even/odd number checking by using bitwise operators. Don't ask me how it works, I just found this out by experimenting with it (could the editor possibly explain?)
if ((1&$num)) {
echo "$num is odd";
}
if (!(1&$num)) {
echo "$num is even";
}
How it works is (1&$num) returns a 1 for odd numbers and returns 0 when it's an even number.`
php at casaforge dot com (Hal)
31-Jan-2003 05:25
`This might be useful in generating fractional numbers for construction, if only because most carpenters would rather put a nail in your foot than hear about any number that ends with .8125".
Since I couldn't figure out the fraction code above, this is my simple-minded take on the problem. Also, align by "char" doesn't seem to work yet in html, so it seems necessary to use tables (egad!) to make numbers align properly. The following code illustrates a way to make a dynamically sized table with aligned fractions from an array of random numbers. Since I don't care about fractions less than 1/16, this rounds them into oblivion. Also, it sorts the list from long to short and collates multiples in the array. One bit of cleverness here (gleaned from these pages) that might not be obvious: I'm using 1 *bitwise and* (1 &) to determine odd numbers.
If you copy and paste the following code, try refreshing the page a few times to see how the table adjusts itself.
<?php
// get some numbers to play with
$x = rand(0,130000)/10;
$y = rand(0,1200);
$z = rand(0,4)/64;
$array = array($x, $x, $x, $y, $y, $z, 324.19, 425/7, sqrt(2), pi(), pi());
// functions
function mult($n) { return intval (round ($n*16)); }
function frac($num) { $mod = fmod ($num,1)*16;
if (1 & $mod) { return " - ".$mod."/16"; }
else $mod = $mod/2;
if (1 & $mod) { return " - ".$mod."/8"; }
else $mod = $mod/2;
if (1 & $mod) { return " - ".$mod."/4"; }
else $mod = $mod/2;
if (1 & $mod) {return " - ".$mod."/2";}
}
// make a table
echo '<table>';
$array = array_map("mult", $array);
$array = (array_filter($array, strval)); //get rid of zeros
$array = (array_count_values ($array));
krsort ($array);
while (list ($key, $val) = each ($array)) {
$key = $key/16;
echo "<tr><td>$val</td><td>&nbsp; @ &nbsp;</td><td align=\"right\">".intval($key)." </td><td> ".frac($key)." </td></tr>";
}
echo '</table>';
?>`
nazgul26 (at_sign) windfox dot net
08-Dec-2002 02:58
`This code will convert a decimal to it's fraction equivalent. The precision can be set by changing PRECISION.
<?php
define(PRECISION, .01);
$count=0;
$result=array();
decimalToFraction($_REQUEST['dec'],$count,&$result);
$count = count($result);
$simp_fract = simplifyFraction($result,$count,1,$result[$count]);
echo $simpl_fract;
// Start of functions
/*
Converts a decimal to unsimplified fraction represented in an array
*/
function decimalToFraction($decimal,$count,$result) {
$a = (1/$decimal);
$b = ( $a - floor($a) );
$count++;
if ($b > .01 && $count <= 5) decimalToFraction($b,$count,&$result);
$result[$count] = floor($a);
}
/*
Simplifies a fraction in an array form that is returned from
decimalToFraction
*/
function simplifyFraction($fraction,$count,$top,$bottom) {
$next = $fraction[$count-1];
$a = ($bottom * $next) + $top;
$top = $bottom;
$bottom = $a;
$count--;
if ($count > 0) simplifyFraction($fraction,$count,$top,$bottom);
else {
return "<font size=1>$bottom/$top</font>";
}
}
?>`
jbeardsl at gte dot net
09-Nov-2002 10:36
`I needed a truncate function to operate on real numbers. I preferred not to use a string-manipulation method, so here's my solution. HTH...
function truncate ($num, $digits = 0) {
//provide the real number, and the number of
//digits right of the decimal you want to keep.
$shift = pow(10 , $digits);
return ((floor($num * $shift)) / $shift);
}`
jbeardsl [found_at] gte [d0t] net
08-Nov-2002 01:15
`I was looking for a truncate function. Not finding one, I wrote my own. Since it deals with everything as a number, I imagine it's faster than the alternative of using string functions. HTH...
<?php
function truncate ($num, $digits = 0) {
//provide the real number, and the number of
//digits right of the decimal you want to keep.
$shift = pow(10, $digits);
return ((floor($num * $shift)) / $shift);
}
?>`
patience at worldonline dot nl
05-Aug-2002 09:08
`The example for Factorials given above is wrong. Here a correct version, so that you do not have to reinvent the wheel again...
<?php
function mathFact( $s )
{
$r = (int) $s;
if ( $r < 2 )
$r = 1;
else {
for ( $i = $r-1; $i > 1; $i-- )
$r = $r * $i;
}
return( $r );
}
?>`
shanx at shanx dot com
08-Jul-2002 01:13
`<?
/**
* Function to calculate base36 values from a number. Very
* useful if you wish to generate IDs from numbers.
*
* @param $value The number
* @param $base The base to be applied (16, 36 or 64)
* @return The calculated string
* @author Shashank Tripathi (shanx@shanx.com)
* @version 0.1 - Let me know if something doesnt work
*
*/
function base36($value, $base)
{
$baseChars = array('0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', 'a', 'b',
'c', 'd', 'e', 'f', 'g', 'h',
'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't',
'u', 'v', 'w', 'x', 'y', 'z'
);
$remainder = 0;
$newval = "";
while ( $value > 0 )
{
$remainder = $value % $base;
$value = ( ($value - $remainder)/ $base );
$newval .= $baseChars[$remainder];
}
return strrev($newval);
}
echo "The string for 46655, for instance, is " . base36(46655, 36);
?>`
webkid%webkid.com
31-May-2002 03:54
`And the reason I needed a Factorial function is because I there were no nPr or nCr functions native to PHP, either.
function n_pick_r($n,$r){$n=(int)$n; $r=(int)$r;return (fact($n)/fact($n-$r));}
function n_choose_r($n,$r){$n=(int)$n; $r=(int)$r;return (n_pick_r($n,$r)/fact($r));}
Hope that helps someone!`
webkid%webkid.com
31-May-2002 03:49
`I found it kind of irritating that PHP had no native functionality for a calculating Factorials. Since I really didn't feel like loading the GMP library, I figured I'd write my own function.
function fact($s){$r=(int)$s; for ($i=$r;$i--;$i>1){$r=$r*$i;} return $r;}
I think that's right... I havn't tested it extensively but it should work.`
cornelius at skjoldhoej dot dk
12-Jun-2001 02:03
`I found that when dealing with tables, a 'least common multiple' function is sometimes useful for abusing tablespan and the likes.
So here goes (you may choose to remove the first part of the gcd function if the function call is well-behaved):
<?php
function gcd(n, m) //greatest common divisor
{
n=abs(n); m=abs(m);
if (n==0 and m==0)
return 1; //avoid infinite recursion
if (n==m and n>=1)
return n;
return m<n?gcd(n-m,n):gcd(n,m-n);
}
function lcm(n, m) //least common multiple
{
return m*(n/gcd(n,m));
}
?>
This may or may not be something to consider adding to the mathematical function library.`
ian at mp3 dot com
19-Feb-2001 03:43
`for those looking for a credit card verification function i wrote a simple LUHN Formula algorithm:
<?php
$valid = 1;
$numOfDigits = 0 - strlen($ccNumber);
$i = -1;
while ($i>=$numOfDigits){
if (($i % 2) == 0){
$double = 2*(substr($ccNumber, $i, 1));
$total += substr($double,0,1);
if (strlen($double > 1)){
$total += substr($double,1,1);
}
} else {
$total += substr($ccNumber, $i, 1);
}
$i--;
}
if (($total % 10) != 0){
$valid = 0;
}
?>`
cathody at mail dot ru
10-Aug-2000 07:55
`Converting non-standard form:
you can use something like this:
<?php
$v=0.3e-9;
$v=sprintf ( "%2.9f", $v);
?>`
add a note
abs mailparse_uudecode_all

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