110 lines
2.5 KiB
Markdown
110 lines
2.5 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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# Binary Logarithm
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> Evaluate the [binary logarithm][binary-logarithm].
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<section class="intro">
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The [binary logarithm][binary-logarithm] (logarithm with base 2) is defined for any positive real number as
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<!-- <equation class="equation" label="eq:binary_logarithm" align="center" raw="\quad \log_{2} \left( x \right) = y \quad \text{such that} \quad 2^y = x" alt="Equation for the binary logarithm."> -->
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<div class="equation" align="center" data-raw-text="\quad \log_{2} \left( x \right) = y \quad \text{such that} \quad 2^y = x" data-equation="eq:binary_logarithm">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@8cb4d022f6163be6523964802725ed2a74f2497b/lib/node_modules/@stdlib/math/base/special/log2/docs/img/equation_binary_logarithm.svg" alt="Equation for the binary logarithm.">
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<br>
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</div>
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<!-- </equation> -->
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var log2 = require( '@stdlib/math/base/special/log2' );
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```
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#### log2( x )
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Evaluates the [binary logarithm][binary-logarithm].
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```javascript
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var v = log2( 4.0 );
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// returns 2.0
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v = log2( 0.0 );
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// returns -Infinity
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v = log2( Infinity );
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// returns Infinity
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v = log2( NaN );
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// returns NaN
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```
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For negative numbers, the [binary logarithm][binary-logarithm] is **not** defined.
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```javascript
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var v = log2( -4.0 );
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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 randu = require( '@stdlib/random/base/randu' );
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var round = require( '@stdlib/math/base/special/round' );
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var log2 = require( '@stdlib/math/base/special/log2' );
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var x;
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var i;
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for ( i = 0; i < 100; i++ ) {
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x = round( randu() * 100.0 );
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console.log( 'log2(%d) = %d', x, log2( x ) );
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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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[binary-logarithm]: https://en.wikipedia.org/wiki/Binary_logarithm
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</section>
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<!-- /.links -->
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