# PHP Science Programming

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factorials

Back to: INDEX | Arbitrary-Precision Math

## Factorials

This function computes the factorial of any positive integer N. This function should be used with caution because the values of factorials can rapidly grow very, very large. For this reason, the function has a built-in limit of N=9999. This limit can be removed, but it is not recommended. Mathematically, the factorial of integer N is simply the product of all the sequential integers from 1 to N multiplied together. Zero factorial equates to 1, by definition. Physically, N factorial represents a count of the total number of possible unique linear sequences (permutations) we can make using N distinct items.

Factorial Calculator based on the function defined below.

With factorial permutations, the only thing that matters is the sequential order of the items. For example, there are 6 unique permutations of 3 people, which is to say that there are (3 x 2 x 1) = 6 ways that 3 people can be lined up in a row. There are (5 x 4 x 3 x 2 x 1) = 120 permutations of 5 people or 120 possible different sequences in which 5 people can be lined up in a row, etc.

Large values can take several seconds to compute in arbitrary-precision, depending on the computer, because they are exact values and could extend out to tens of thousands of digits in some cases. For example, 100 factorial equates to a 158-digit integer and at the limit of 9999 factorial, its value equates to a 35656-digit integer!

Beyond the set limit, there is a possibility of a script-timeout error or an otherwise prohibitively long wait for the result. Different web servers on which you may run a program may apply different script-time-out limits (typically 30 seconds, but it can usually be extended).

```/*
===========================================================================
This function returns the arbitrary-precision factorial of any non-negative
integer value.  This function should be used with caution, since factorial
values can be extremely large for relatively small arguments.  It may take
several seconds to compute extremely large factorials (e.g. > 10000!), so
a safety limit of 9999 is built in, but it can be easily removed.

Input argument must be a positive integer.  Any decimal argument will be
silently truncated to an integer, without rounding, rather than causing
an error.

ERRORS:
FALSE is returned on error, if argument is non-numeric or negative or
argument exceeds maximum set limit (default = 9999).
===========================================================================
*/

function bcN_Factorial (\$N=0)
{
// Error if argument N is non-numeric, negative or > 9999.
if (!is_numeric(\$N)) {return FALSE;}

// Truncate any decimal argument to an
// integer value, without rounding.
\$n = bcadd(\$N, 0);

// Error if argument outside valid range (0 to 9999).
if (\$n < 0 or \$n > 9999) {return FALSE;}

// Execute loop to compute N factorial product (P).
\$P=1;  for (\$i=1;  \$i <= \$n;  \$i++) {\$P = bcmul(\$P, \$i);}

// Done.
return \$P;
}```

Running the following example program produces the table of factorials from 1 to 64 that follows.

```<?php

/*
This program demonstrates the computation of exact integer
factorial values using arbitrary-precision arithmetic.

AUTHOR: Jay Tanner
*/

// ------------------------------------------------------
// Compute table of EXACT integer factorials from 1 to N!

\$N = 64;

\$FactorialTable = "";

for(\$n=1;   \$n <= \$N;   \$n++)
{
\$F=1;  for (\$i=1;  \$i <= \$n;  \$i++) {\$F = bcmul(\$F, \$i);}

\$FactorialTable .=  substr(\$n . str_repeat(" ", 4), 0, 4) . "\$F\n";
}

// Print out the computed table.
print "<b><pre>\nN   N!\n\$FactorialTable</pre></b>\n";

?>
```

```N   N!
1   1
2   2
3   6
4   24
5   120
6   720
7   5040
8   40320
9   362880
10  3628800
11  39916800
12  479001600
13  6227020800
14  87178291200
15  1307674368000
16  20922789888000
17  355687428096000
18  6402373705728000
19  121645100408832000
20  2432902008176640000
21  51090942171709440000
22  1124000727777607680000
23  25852016738884976640000
24  620448401733239439360000
25  15511210043330985984000000
26  403291461126605635584000000
27  10888869450418352160768000000
28  304888344611713860501504000000
29  8841761993739701954543616000000
30  265252859812191058636308480000000
31  8222838654177922817725562880000000
32  263130836933693530167218012160000000
33  8683317618811886495518194401280000000
34  295232799039604140847618609643520000000
35  10333147966386144929666651337523200000000
36  371993326789901217467999448150835200000000
37  13763753091226345046315979581580902400000000
38  523022617466601111760007224100074291200000000
39  20397882081197443358640281739902897356800000000
40  815915283247897734345611269596115894272000000000
41  33452526613163807108170062053440751665152000000000
42  1405006117752879898543142606244511569936384000000000
43  60415263063373835637355132068513997507264512000000000
44  2658271574788448768043625811014615890319638528000000000
45  119622220865480194561963161495657715064383733760000000000
46  5502622159812088949850305428800254892961651752960000000000
47  258623241511168180642964355153611979969197632389120000000000
48  12413915592536072670862289047373375038521486354677760000000000
49  608281864034267560872252163321295376887552831379210240000000000
50  30414093201713378043612608166064768844377641568960512000000000000
51  1551118753287382280224243016469303211063259720016986112000000000000
52  80658175170943878571660636856403766975289505440883277824000000000000
53  4274883284060025564298013753389399649690343788366813724672000000000000
54  230843697339241380472092742683027581083278564571807941132288000000000000
55  12696403353658275925965100847566516959580321051449436762275840000000000000
56  710998587804863451854045647463724949736497978881168458687447040000000000000
57  40526919504877216755680601905432322134980384796226602145184481280000000000000
58  2350561331282878571829474910515074683828862318181142924420699914240000000000000
59  138683118545689835737939019720389406345902876772687432540821294940160000000000000
60  8320987112741390144276341183223364380754172606361245952449277696409600000000000000
61  507580213877224798800856812176625227226004528988036003099405939480985600000000000000
62  31469973260387937525653122354950764088012280797258232192163168247821107200000000000000
63  1982608315404440064116146708361898137544773690227268628106279599612729753600000000000000
64  126886932185884164103433389335161480802865516174545192198801894375214704230400000000000000
```
By examining the above table, one can see how rapidly the values of factorials increase.

factorials.txt · Last modified: 2014/05/24 04:34 by Jay.Tanner.x@PHPScienceLabs.us

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