logaddexp
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.
Usage
var logaddexp = require( '@stdlib/math/base/special/logaddexp' );
logaddexp( x, y )
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
Examples
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 );
}
}
C APIs
Usage
#include "stdlib/math/base/special/logaddexp.h"
stdlib_base_logaddexp( x, y )
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] doubleinput value. - y:
[in] doubleinput value.
double stdlib_base_logaddexp( const double x, const double y );
Examples
#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 );
}
}