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expm1 deg2rad

Last updated: Sat, 27 Jan 2007

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# exp

(PHP 3, PHP 4, PHP 5)

exp -- Calculates the exponent of `e`

## Description

float exp ( float arg )

Returns `e` raised to the power of `arg`.

> Замечание: 'e' is the base of the natural system of logarithms, or approximately 2.718282.

Пример 1. exp() example

`<?php echo exp(12) . "\n"; echo exp(5.7); ?>`

Результат выполнения данного примера:

    1.6275E+005
    298.87

See also log() and pow().

add a note User Contributed Notes
exp
konrad
24-Jan-2007 03:13
`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 $sum;
}
?>`
boards at gmail dot com
26-Apr-2006 10:18
`Note regarding the mathematical function exp(x):
To continue accuracy of the exponential function to an infinite amount of decimal places, one would use the power series definition for exp(x).
(in LaTeX form:)
e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}
So, to do that in PHP (using BC math):
<?php
// arbitrary precision function (x^n)/(n)!
function bcpowfact($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 $a;
}
// arbitrary precision exp() function
function bcexp($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;
}
?>`
info at teddycaddy dot com
16-Sep-2004 06:55
`This only returns the first 51 digits after the decimal point.`
add a note
expm1 deg2rad

Last updated: Sat, 27 Jan 2007
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Last updated: Sat Mar 10 09:32:46 2007 PST