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Evaluates the natural logarithm of
exp(x) + exp(y)
.
Log-domain computations are commonly used to increase accuracy and avoid underflow and overflow when very small or very large numbers are represented directly as limited-precision, floating-point numbers. For example, in statistics, evaluating logaddexp()
is useful when probabilities are so small as to exceed the normal range of floating-point numbers.
npm install @stdlib/math-base-special-logaddexp
var logaddexp = require( '@stdlib/math-base-special-logaddexp' );
Evaluates the natural logarithm of exp(x) + exp(y)
.
var v = logaddexp( 90.0, 90.0 );
// returns ~90.6931
v = logaddexp( -20.0, 90.0 );
// returns 90.0
v = logaddexp( 0.0, -100.0 );
// returns ~3.7201e-44
v = logaddexp( NaN, 1.0 );
// returns NaN
var incrspace = require( '@stdlib/array-base-incrspace' );
var logaddexp = require( '@stdlib/math-base-special-logaddexp' );
var x = incrspace( -100.0, 100.0, 1.0 );
var v;
var i;
var j;
for ( i = 0; i < x.length; i++ ) {
for ( j = i; j < x.length; j++ ) {
v = logaddexp( x[ i ], x[ j ] );
console.log( 'x: %d, y: %d, f(x, y): %d', x[ i ], x[ j ], v );
}
}
#include "stdlib/math/base/special/logaddexp.h"
Evaluates the natural logarithm of exp(x) + exp(y)
.
double out = stdlib_base_logaddexp( 90.0, 90.0 );
// returns ~90.6931
out = stdlib_base_logaddexp( -20.0, 90.0 );
// returns 90.0
The function accepts the following arguments:
-
x:
[in] double
input value. -
y:
[in] double
input value.
double stdlib_base_logaddexp( const double x, const double y );
#include "stdlib/math/base/special/logaddexp.h"
#include <stdlib.h>
#include <stdio.h>
int main( void ) {
double x;
double y;
double v;
int i;
for ( i = 0; i < 100; i++ ) {
x = ( ( (double)rand() / (double)RAND_MAX ) * 200.0 ) - 100.0;
y = ( ( (double)rand() / (double)RAND_MAX ) * 200.0 ) - 100.0;
v = stdlib_base_logaddexp( x, y );
printf( "x: %lf, y: %lf, logaddexp(x, y): %lf\n", x, y, v );
}
}
-
@stdlib/math-base/special/exp
: natural exponential function. -
@stdlib/math-base/special/ln
: evaluate the natural logarithm of a double-precision floating-point number.
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.
See LICENSE.
Copyright © 2016-2024. The Stdlib Authors.