PHP 5.6.0beta1 released

Math Functions

Table of Contents

  • abs — مقدار قدر مطلق
  • acos — Arc cosine
  • acosh — Inverse hyperbolic cosine
  • asin — Arc sine
  • asinh — Inverse hyperbolic sine
  • atan2 — Arc tangent of two variables
  • atan — Arc tangent
  • atanh — Inverse hyperbolic tangent
  • base_convert — Convert a number between arbitrary bases
  • bindec — Binary to decimal
  • ceil — Round fractions up
  • cos — Cosine
  • cosh — Hyperbolic cosine
  • decbin — Decimal to binary
  • dechex — Decimal to hexadecimal
  • decoct — دهدهی به هشت هشتی
  • deg2rad — Converts the number in degrees to the radian equivalent
  • exp — Calculates the exponent of e
  • expm1 — Returns exp(number) - 1, computed in a way that is accurate even when the value of number is close to zero
  • floor — Round fractions down
  • fmod — Returns the floating point remainder (modulo) of the division of the arguments
  • getrandmax — Show largest possible random value
  • hexdec — Hexadecimal to decimal
  • hypot — Calculate the length of the hypotenuse of a right-angle triangle
  • is_finite — Finds whether a value is a legal finite number
  • is_infinite — یافتن بینهایت بودن مقدار
  • is_nan — یافتن عدد بودن یک مقدار
  • lcg_value — Combined linear congruential generator
  • log10 — Base-10 logarithm
  • log1p — Returns log(1 + number), computed in a way that is accurate even when the value of number is close to zero
  • log — Natural logarithm
  • max — Find highest value
  • min — Find lowest value
  • mt_getrandmax — Show largest possible random value
  • mt_rand — Generate a better random value
  • mt_srand — Seed the better random number generator
  • octdec — Octal to decimal
  • pi — Get value of pi
  • pow — Exponential expression
  • rad2deg — Converts the radian number to the equivalent number in degrees
  • rand — Generate a random integer
  • round — Rounds a float
  • sin — Sine
  • sinh — Hyperbolic sine
  • sqrt — ریشه مربعی
  • srand — Seed the random number generator
  • tan — تانژانت
  • tanh — Hyperbolic tangent
add a note add a note

User Contributed Notes 48 notes

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3
capripot at gmail dot com
1 year ago
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.
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3
jerry dot wilborn at fast dot net
10 years ago
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) / $sample_count), 2));
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3
bjcffnet at gmail dot com
8 years ago
thearbitcouncil at gmail dot com, you could just use array_sum():
<?php
function average($arr)
{
   if (!
is_array($arr)) return false;

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

$array = array(5, 10, 15);
echo
average($array); // 10
?>
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3
edward at edwardsun dot com
7 years ago
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.
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2
webkid%webkid.com
11 years ago
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!
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1
Mike
6 years ago
//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 $newInteger;
}
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1
tmpa at yahoo dot com
9 years ago
while joogat's one line function is short, it is probably better to calculate factorial iteratively instead of recursively. keep in mind if you want large factorials, you'll need to use some sort of arbitrary precision integer or perhaps the BCMath functions. then again, unless you're trying to do large numbers (170! is the highest that you can do that does not return infinity) you probably won't notice any time difference.
<?php
function factorial($in) {
   
// 0! = 1! = 1
   
$out = 1;

   
// Only if $in is >= 2
   
for ($i = 2; $i <= $in; $i++) {
       
$out *= $i;
    }

    return
$out;
}
?>
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2
php at keith tyler dot com
3 years ago
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)));'
?>
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2
lummox
6 years ago
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);
}
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2
thearbitcouncil at gmail dot com
9 years ago
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 :)

?>
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2
jbeardsl [found_at] gte [d0t] net
11 years ago
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);
}
?>
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1
eric at woolhiser dot com
9 years ago
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);

}
?>
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1
help at gjbdesign dot com
9 years ago
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
   
}
}
?>
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1
Chronial "at" cyberpunkuniverse.de
10 years ago
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;
}
?>
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1
chris at free-source dot com
10 years ago
to "convert" scientific notation to a float simply cast it:
<?php
$val
= '3.5e4';
$val = (float) $val;
echo
$val;
?>

output:
35000
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1
patience at worldonline dot nl
11 years ago
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 );
}
?>
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0
AsherMaximum gmail
2 years ago
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' : $i.'th') ) ) )
?>
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0
rubo77 at spacetrace dot org
5 years ago
<?php
function lcd($n,$m, $maxvarianzpercent=0){
   
// set $maxvarianzpercent=5 to get a small, but approx. result
    /* a better lcd function with varianz:
    for example use
    lcd(141,180,5) to get the approx. lcd '7/9' which is in fact 140/180
    */
    // ATTENTION!!! can be really slow if $m is >1000
   
   
$d=$n/$m;
   
$f=1;
    while(
$d*$f!=intval($d*$f)){
       
$f++;
    }
   
$r=($d*$f).'/'.$f;
    if((
$d*$f)<=10 or $f<=10) return $r;
    else if(
$maxvarianzpercent>0){
       
$f=1;
        while(
$d*$f!=intval($d*$f) and ($d*$f)-intval($d*$f) > $maxvarianzpercent/100){
           
$f++;
        }
        return
intval($d*$f).'/'.$f;
    } else return
$r;
}
?>
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0
ddarjany at yahoo dot com
6 years ago
Tim's fix of Evan's ordinal function causes another problem, it no longer works for number above 100.  (E.g. it returns 111st instead of 111th). 
Here is a further modified version which should work for all numbers.

<?PHP

function ordinal($cardinal)    {
 
$cardinal = (int)$cardinal;
 
$digit = substr($cardinal, -1, 1);

  if (
$cardinal <100) $tens = round($cardinal/10);
  else
$tens = substr($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';
  }
}
 
?>
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0
barry at megaspace dot com
7 years ago
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);
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0
tim at durge dot org
7 years ago
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.
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0
twoscoopsofpig at NOSPAM dot gmail dot com
7 years ago
@ Moikboy:

This may or may not be more simplified factorialization:

<?php
$f
=$fact=25;
while (
$fact>0)
{
$f=$f*$fact--;}
echo
$f;
?>
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0
marasek.SPAMLESS at telton.de
7 years ago
I could not resist to do a simpler version of the ordinal function:
<?php
function ordinal($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.
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0
moikboy (nospam!) moikboy (nospam!) hu
7 years ago
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[$int];
};
?>
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0
Florian
8 years ago
A function that simulates the sum operator. (http://en.wikipedia.org/wiki/Sum). Be careful with the expression because it may cause a security hole; note the single quotes to don't parse the "$".
<?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;
}
?>
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0
jos at gtacrime dot nl
8 years ago
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;
}
?>
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0
daniel at g-loc dot org
8 years ago
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!
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0
graywh at gmail DELETE dot com
8 years ago
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))
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0
info at gavinvincent dot co dot uk
9 years ago
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;
 }
}
?>
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0
donnieb819 at hotmail dot NOSPAM dot com
9 years ago
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
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0
pat.mat AT sympatico DOT com
9 years ago
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
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0
ausvald at tut dot by
9 years ago
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;
}
?>
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0
florian at shellfire dot de
9 years ago
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));   
    }

?>
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0
jl85 at yahoo dot com
10 years ago
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));
}
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0
fabien_mornand at yahoo dot fr
10 years ago
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;
?>
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0
matthew_gaddis at yahoo dot com
10 years ago
Here is a cleaner factorial function:

function factorial($s){
    if($s) $r = $s * factorial($s - 1);
    else $r = 1;
    return $r;
}
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0
jl85 at yahoo dot com
11 years ago
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.
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0
nazgul26 (at_sign) windfox dot net
11 years ago
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>";
    }
}
?>
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0
jbeardsl at gte dot net
11 years ago
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);

}
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0
shanx at shanx dot com
11 years ago
<?

/**
 * 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);

?>
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0
webkid%webkid.com
11 years ago
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.
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0
ian at mp3 dot com
13 years ago
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;
}
?>
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-1
tembenite at gmail dot com
7 years ago
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));
}
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-1
jordanolsommer at imap dot cc
10 years ago
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 :).
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-1
Evan Broder
7 years ago
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';
        }
    }

?>
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-1
peter-stangl at t-online dot de
8 years ago
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');
   }
}

?>
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-1
monte at ohrt dot com
8 years ago
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++);
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-1
cornelius at skjoldhoej dot dk
12 years ago
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.
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