Logarithm

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

Installation

npm install @stdlib/math-base-special-log

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

• @stdlib/math-base/special/exp: natural exponential function.
• @stdlib/math-base/special/ln: evaluate the natural logarithm of a double-precision floating-point number.
• @stdlib/math-base/special/log10: common logarithm (base ten).
• @stdlib/math-base/special/log1p: evaluate the natural logarithm of 1+x.
• @stdlib/math-base/special/log2: binary logarithm (base 2).

Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.