factorial
Factorial function.
The factorial function may be defined as the product
or according to the recurrence relation
Following the convention for an empty product, in all definitions,
The Gamma function extends the factorial function for non-integer values.
The factorial of a negative integer is not defined.
Usage
var factorial = require( '@stdlib/math/base/special/factorial' );
factorial( x )
Evaluates the factorial function.
var v = factorial( 3.0 );
// returns 6.0
v = factorial( -1.5 );
// returns ~-3.545
v = factorial( -0.5 );
// returns ~1.772
v = factorial( 0.5 );
// returns ~0.886
v = factorial( -10.0 );
// returns NaN
v = factorial( 171.0 );
// returns Infinity
v = factorial( NaN );
// returns NaN
Examples
var incrspace = require( '@stdlib/array/base/incrspace' );
var factorial = require( '@stdlib/math/base/special/factorial' );
var x = incrspace( -10.0, 100.0, 1.0 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( 'x: %d, f(x): %d', x[ i ], factorial( x[ i ] ) );
}
C APIs
Usage
#include "stdlib/math/base/special/factorial.h"
stdlib_base_factorial( x )
Evaluates the factorial function.
double out = stdlib_base_factorial( 3.0 );
// returns 6.0
out = stdlib_base_factorial( -1.5 );
// returns ~-3.545
The function accepts the following arguments:
- x:
[in] doubleinput value.
double stdlib_base_factorial( const double n );
Examples
#include "stdlib/math/base/special/factorial.h"
#include <stdio.h>
int main( void ) {
const double x[] = { 2.0, 3.0, 5.0, 8.0 };
double y;
int i;
for ( i = 0; i < 4; i++ ) {
y = stdlib_base_factorial( x[ i ] );
printf( "factorial(%lf) = %lf\n", x[ i ], y );
}
}