log1p

Evaluate the natural logarithm of 1+x.

Usage

var log1p = require( '@stdlib/math/base/special/log1p' );

log1p( x )

Evaluates the natural logarithm of 1+x.

var v = log1p( 4.0 );
// returns ~1.609

v = log1p( -1.0 );
// returns -Infinity

v = log1p( Infinity );
// returns Infinity

v = log1p( 0.0 );
// returns 0.0

v = log1p( -0.0 );
// returns -0.0

v = log1p( NaN );
// returns NaN

For x < -1, the function returns NaN, as the natural logarithm is not defined for negative numbers.

var v = log1p( -2.0 );
// returns NaN

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var log1p = require( '@stdlib/math/base/special/log1p' );

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

logEachMap( 'log1p( %0.4f ) = %0.4f', x, log1p );

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C APIs

Usage

#include "stdlib/math/base/special/log1p.h"

stdlib_base_log1p( x )

Evaluates the natural logarithm of 1+x.

double out = stdlib_base_log1p( 4.0 );
// returns ~1.609

out = stdlib_base_log1p( -1.0 );
// returns -Infinity

The function accepts the following arguments:

• x: [in] double input value.

double stdlib_base_log1p( const double x );

Examples

#include "stdlib/math/base/special/log1p.h"
#include <stdlib.h>
#include <stdio.h>

int main( void ) {
    double x;
    double v;
    int i;

    for ( i = 0; i < 100; i++ ) {
        x = ( (double)rand() / (double)RAND_MAX ) * 100.0;
        v = stdlib_base_log1p( x );
        printf( "log1p(%lf) = %lf\n", x, v );
    }
}

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See Also

• @stdlib/math/base/special/ln: evaluate the natural logarithm of a double-precision floating-point number.
• @stdlib/math/base/special/log: compute the base b logarithm of a double-precision floating-point number.