Compute the natural logarithm of exp(x) + exp(y).
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> Evaluates the [natural logarithm][@stdlib/math/base/special/ln] 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.
``bash`
npm install @stdlib/math-base-special-logaddexp
`javascript`
var logaddexp = require( '@stdlib/math-base-special-logaddexp' );
#### logaddexp( x, y )
Evaluates the [natural logarithm][@stdlib/math/base/special/ln] of exp(x) + exp(y).
`javascript
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
`
`javascript
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`
#include "stdlib/math/base/special/logaddexp.h"
#### stdlib_base_logaddexp( x, y )
Evaluates the [natural logarithm][@stdlib/math/base/special/ln] of exp(x) + exp(y).
`c
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.[in] double
- y: input value.
`c`
double stdlib_base_logaddexp( const double x, const double y );
`c
#include "stdlib/math/base/special/logaddexp.h"
#include
#include
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][@stdlib/math/base/special/exp]: natural exponential function.
- [@stdlib/math-base/special/ln][@stdlib/math/base/special/ln]: evaluate the natural logarithm of a double-precision floating-point number.
*
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
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---
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[@stdlib/math/base/special/exp]: https://www.npmjs.com/package/@stdlib/math-base-special-exp
[@stdlib/math/base/special/ln]: https://www.npmjs.com/package/@stdlib/math-base-special-ln