digamma
Digamma function.
The digamma function ψ is the logarithmic derivative of the gamma function, i.e.
Usage
var digamma = require( '@stdlib/math/base/special/digamma' );
digamma( x )
Evaluates the digamma function.
var v = digamma( -2.5 );
// returns ~1.103
v = digamma( 1.0 );
// returns ~-0.577
v = digamma( 10.0 );
// returns ~2.252
If x is 0 or a negative integer, the function returns NaN.
var v = digamma( 0.0 );
// returns NaN
v = digamma( -1.0 );
// returns NaN
v = digamma( -2.0 );
// returns NaN
If provided NaN, the function returns NaN.
var v = digamma( NaN );
// returns NaN
Examples
var randu = require( '@stdlib/random/base/randu' );
var digamma = require( '@stdlib/math/base/special/digamma' );
var x;
var v;
var i;
for ( i = 0; i < 10; i++ ) {
x = (randu()*10.0) - 5.0;
v = digamma( x );
console.log( 'x: %d, f(x): %d', x, v );
}
C APIs
Usage
#include "stdlib/math/base/special/digamma.h"
stdlib_base_digamma( x )
Evaluates the digamma function.
double out = stdlib_base_digamma( -2.5 );
// returns ~1.103
out = stdlib_base_digamma( 1.0 );
// returns ~-0.577
The function accepts the following arguments:
- x:
[in] doubleinput value.
double stdlib_base_digamma( const double x );
Examples
#include "stdlib/math/base/special/digamma.h"
#include <stdlib.h>
#include <stdio.h>
int main( void ) {
const double x[] = { 4.0, -1.5, -0.5, 0.5 };
double y;
int i;
for ( i = 0; i < 4; i++ ) {
y = stdlib_base_digamma( x[ i ] );
printf( "digamma(%lf) = %lf\n", x[ i ], y );
}
}