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README.md

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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var log = require( '@stdlib/math/base/special/log' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 100, 0, 100, opts );
var b = discreteUniform( 100, 0, 5, opts );

logEachMap( 'log( %0.4f, %0.4f ) = %0.4f', x, b, log );

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 );
    }
}

See Also