Math 函数

Table of Contents

  • abs — 绝对值
  • acos — 反余弦
  • acosh — 反双曲余弦
  • asin — 反正弦
  • asinh — 反双曲正弦
  • atan2 — 两个参数的反正切
  • atan — 反正切
  • atanh — 反双曲正切
  • base_convert — 在任意进制之间转换数字
  • bindec — 二进制转换为十进制
  • ceil — 进一法取整
  • cos — 余弦
  • cosh — 双曲余弦
  • decbin — 十进制转换为二进制
  • dechex — 十进制转换为十六进制
  • decoct — 十进制转换为八进制
  • deg2rad — 将角度转换为弧度
  • exp — 计算 e 的指数
  • expm1 — 返回 exp(number) - 1,甚至当 number 的值接近零也能计算出准确结果
  • fdiv — Divides two numbers, according to IEEE 754
  • floor — 舍去法取整
  • fmod — 返回除法的浮点数余数
  • getrandmax — 显示随机数最大的可能值
  • hexdec — 十六进制转换为十进制
  • hypot — 计算一直角三角形的斜边长度
  • intdiv — 对除法结果取整
  • is_finite — 判断是否为有限值
  • is_infinite — 判断是否为无限值
  • is_nan — 判断是否为合法数值
  • lcg_value — 组合线性同余发生器
  • log10 — 以 10 为底的对数
  • log1p — 返回 log(1 + number),甚至当 number 的值接近零也能计算出准确结果
  • log — 自然对数
  • max — 找出最大值
  • min — 找出最小值
  • mt_getrandmax — 显示随机数的最大可能值
  • mt_rand — 生成更好的随机数
  • mt_srand — 播下一个更好的随机数发生器种子
  • octdec — 八进制转换为十进制
  • pi — 得到圆周率值
  • pow — 指数表达式
  • rad2deg — 将弧度数转换为相应的角度数
  • rand — 产生一个随机整数
  • round — 对浮点数进行四舍五入
  • sin — 正弦
  • sinh — 双曲正弦
  • sqrt — 平方根
  • srand — 播下随机数发生器种子
  • tan — 正切
  • tanh — 双曲正切

User Contributed Notes

pradhumansaini2 at gmail dot com 06-Mar-2021 06:17
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Anonymous 02-Feb-2018 06:44
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!
exmple:https://vb.3dlat.com/
Aiden880 28-Mar-2015 01:47
Lowest Common Denominator:
function lcd($num, $start) {
    while($num % $start != 0) {
        $start++;
    }
    return $start;
}
capripot at gmail dot com 18-Jul-2012 09:48
Another simpler function to check a number with the luhn algorithm :

<?php
function luhn($num){
    if(!
$num)
        return
false;
   
$num = array_reverse(str_split($num));
   
$add = 0;
    foreach(
$num as $k => $v){
        if(
$k%2)
           
$v = $v*2;
       
$add += ($v >= 10 ? $v - 9 : $v);
    }
    return (
$add%10 == 0);
}
?>

Don't know if foreach and arrays operations are faster than while and substr, but I feel it clearer.
AsherMaximum gmail 18-Apr-2011 09:40
Here's a simple way way to convert a number to an ordinal number I created:

$i == the number to convert. Put this inside a for loop if you need to populate an array.

<?php
// change increment variable to ordinal number.
$n1 = $i % 100; //first remove all but the last two digits

$n2 = ($n1 < 20 ? $1 : $i % 10; //remove all but last digit unless the number is in the teens, which all should be 'th'

//$n is now used to determine the suffix.
$ord = ($n2==1 ? $i.'st' : ( ($n2==2 ? $i.'nd' : ($n2==3 ? $i.'rd' : $i.'th') ) ) )
?>
php at keith tyler dot com 04-Nov-2010 11:09
Another ordinal method, which does not involve utilizing date functions:

<?php
sprintf
( "%d%s", $t, array_pop( array_slice( array_merge( array( "th","st","nd","rd"), array_fill( 4,6,"th")), $t%10, 1)));'
?>
lummox 02-Feb-2008 07:24
Wouldn't the following function do the same but a lot easier than the one in the comment before?

function trimInteger($targetNumber,$newLength) {
    return $targetNumber%pow(10,$newLength);
}
Mike 09-Jan-2008 07:23
//had a mistake in last post, heres the corrected version

/*
Just a simple function to trim digits from the left side of an integer. TRIM DOWN TO 4-> (ie. 987654 => 7654)
*/

function trimInteger($targetNumber,$newLength) {

    $digits = pow(10,$newLength);

    $s = ($targetNumber/ $digits); //make the last X digits the                  decimal part

    $t = floor($targetNumber / $digits); //drop the last X digits (the decimal part)

    $h = $s - $t; //remove all  but the decimal part

    $newInteger = ($h*$digits); //make the everything after the decimal point the new number

    return $newInteger;
}
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));
}
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.
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[$int];
};
?>
Florian 03-Mar-2006 01:36
A function that simulates the sum operator. (http://en.wikipedia.org/wiki/Sum). Be careful with the expression because it may cause a security hole; note the single quotes to don't parse the "$".
<?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;
}
?>
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!
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, $j++);
bjcffnet at gmail dot com 26-Jul-2005 04:57
thearbitcouncil at gmail dot com, you could just use array_sum():
<?php
function average($arr)
{
   if (!
is_array($arr)) return false;

   return
array_sum($arr)/count($arr);
}

$array = array(5, 10, 15);
echo
average($array); // 10
?>
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
   
}
}
?>
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
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
    // for 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;
}
?>
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 :).
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.
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 [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 );
}
?>
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!
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;
}
?>