# exp

(PHP 4, PHP 5)

expCalculates the exponent of e

float exp ( float $arg ) Returns e raised to the power of arg. Note: 'e' is the base of the natural system of logarithms, or approximately 2.718282. ### Parameters arg The argument to process ### Return Values 'e' raised to the power of arg ### Examples Example #1 exp() example  <?phpecho exp(12) . "\n";echo exp(5.7);?>  The above example will output: 1.6275E+005 298.87  ### See Also • log() - Natural logarithm • pow() - Exponential expression add a note ### User Contributed Notes 5 notes zooly at globmi dot com 7 years ago  PHP does not have the following math function in any extensions:frexp() - Extract Mantissa and Exponent of the Floating-Point ValueI've digged many C source codes, and found the simplest implementation as follows:<?phpfunction frexp ($float ) {  $exponent = ( floor(log($float, 2)) + 1 );  $mantissa = ($float * pow(2, -$exponent) ); return( array($mantissa, $exponent) );}print_r(frexp(0.0345));print_r(frexp(21.539));?>Array( [0] => 0.552 [1] => -4)Array( [0] => 0.67309375 [1] => 5)I have compared the results using a lot of floats against C's frexp function - they are the same.Note that C and PHP uses different float precisions, for example "4619.3" gives:C: 0.56387939453125, 13PHP: 0.563879394531, 13/Assuming default configurations./  konrad 11 years ago  working version (checked) of below code is <?php // see bccomp for this code (signed and unsigned zero!) function bccomp_zero($amount) {    return bccomp($amount, (@$amount{0}=="-"?'-':'').'0.0');  }  // arbitrary precision function (x^n)/(n)!  function bcpowfact($x,$n) {    if (bccomp_zero($n) == 0) return '1'; if (bccomp($n, '1') == 0) return $x;$a = $x; // 1st step: a *= x / 1$i = $n; while (bccomp($i, '1') == 1) {      // ith step: a *= x / i      $a = bcmul($a, bcdiv($x,$i));      $i = bcsub($i, '1'); // bc idiom for $i-- } return$a;  }  // arbitrary precision exp() function  function bcexp($x,$digits) {    $sum =$prev_sum = '0.0';    $error = '0.'.str_repeat('0',$digits-1).'1'; // 0.1*10^-k    $n = '0.0'; do {$prev_sum = $sum;$sum = bcadd($sum, bcpowfact($x, $n));$n = bcadd($n, '1'); // bc idiom for$n++    } while (bccomp(bcsub($sum,$prev_sum), $error) == 1); return$sum;  }?> 
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12 years ago
 Note regarding the mathematical function exp(x):To continue accuracy of the exponential function to an infinite amount of decimal places, one would use the power series definition for exp(x).(in LaTeX form:)e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}So, to do that in PHP (using BC math):<?php// arbitrary precision function (x^n)/(n)!function bcpowfact($x,$n) {  if (bccomp($n, '0') == 0) return '1.0'; if (bccomp($n, '1') == 1) return $x;$a = $x; // nth step: a *= x / 1$i = $n; while (bccomp($i, '1') == 1) {    // ith step: a *= x / i    $a = bcmul($a, bcdiv($x,$i));    $i = bcsub($i, '1'); // bc idiom for $i-- } return$a;}// arbitrary precision exp() functionfunction bcexp($x,$decimal_places) {  $sum =$prev_sum = '0.0';  $error = bcdiv(bcpow('10', '-'.$decimal_places), 10); // 0.1*10^-k  $n = '0'; do {$prev_sum = $sum;$sum = bcadd($sum, bcpowfact($x, $n)); } while (bccomp(bcsub($sum, $prev_sum),$error) == 1);  return $sum;}?>  -2 Nitrogen 8 years ago  Just a note about using the submitted codes below..Their functions have an optional$precision parameter; however, it's not being used properly..BCMath functions by default do not use decimal precision unless specified by BCScale($precision); or using the extra parameter in the used BC functions.For example, a blank PHP file with their code.. executing BCExp('5.7'); returns "47" instead of the correct answer of "298.86740096706..."So for optimum accuracy, I'd suggest setting BCScale to a healthy length before running their codes.  -7 Mohammed AbdelRahman 3 years ago  Which is the inverse of log(float$arg, e)