Logarithm

Compute the base b logarithm of a double-precision floating-point number.

Usage

var log = require( '@stdlib/math/base/special/log' );

log( x, b )

Computes the base b logarithm of a double-precision floating-point number.

var v = log( 100.0, 10.0 );
// returns 2.0

v = log( 16.0, 2.0 );
// returns 4.0

v = log( 5.0, 1.0 );
// returns Infinity

For negative x or b, the logarithm is not defined.

var v = log( -4.0, 1.0 );
// returns NaN

v = log( 2.0, -4.0 );
// returns NaN

Examples

var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var log = require( '@stdlib/math/base/special/log' );

var b;
var x;
var i;

for ( i = 0; i < 100; i++ ) {
    x = round( randu() * 100.0 );
    b = round( randu() * 5.0 );
    console.log( 'log( %d, %d ) = %d', x, b, log( x, b ) );
}

C APIs

Usage

#include "stdlib/math/base/special/log.h"

stdlib_base_log( x, b )

Computes the base b logarithm of a double-precision floating-point number.

double v = stdlib_base_log( 100.0, 10.0 );
// returns 2.0

The function accepts the following arguments:

x: [in] double input value.
b: [in] double input value.

double stdlib_base_log( const double x, const double b );

Examples

#include "stdlib/math/base/special/log.h"
#include <stdlib.h>
#include <stdio.h>

int main( void ) {
    double out;
    double x;
    double b;
    int i;

    for ( i = 0; i < 100; i++ ) {
        x = ( (double)rand() / (double)RAND_MAX ) * 100.0;
        b = ( (double)rand() / (double)RAND_MAX ) * 5.0;
        out = stdlib_base_log( x, b );
        printf( "log(%lf, %lf) = %lf\n", x, b, out );
    }
}