96 lines
2.2 KiB
Markdown
96 lines
2.2 KiB
Markdown
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# logaddexp
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> Evaluates the [natural logarithm][@stdlib/math/base/special/ln] of `exp(x) + exp(y)`.
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<section class="intro">
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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.
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</section>
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<section class="usage">
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## Usage
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```javascript
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var logaddexp = require( '@stdlib/math/base/special/logaddexp' );
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```
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#### logaddexp( x, y )
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Evaluates the [natural logarithm][@stdlib/math/base/special/ln] of `exp(x) + exp(y)`.
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```javascript
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var v = logaddexp( 90.0, 90.0 );
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// returns ~90.6931
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v = logaddexp( -20.0, 90.0 );
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// returns 90.0
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v = logaddexp( 0.0, -100.0 );
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// returns ~3.7201e-44
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v = logaddexp( NaN, 1.0 );
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// returns NaN
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```
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</section>
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<!-- /.usage -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var incrspace = require( '@stdlib/array/incrspace' );
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var logaddexp = require( '@stdlib/math/base/special/logaddexp' );
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var x;
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var v;
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var i;
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var j;
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x = incrspace( -100.0, 100.0, 1.0 );
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for ( i = 0; i < x.length; i++ ) {
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for ( j = i; j < x.length; j++ ) {
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v = logaddexp( x[ i ], x[ j ] );
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console.log( 'x: %d, y: %d, f(x, y): %d', x[ i ], x[ j ], v );
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}
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}
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[@stdlib/math/base/special/ln]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/ln
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</section>
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<!-- /.links -->
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