190 lines
5.4 KiB
Markdown
190 lines
5.4 KiB
Markdown
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<!--
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@license Apache-2.0
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Copyright (c) 2020 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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# abs2
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> Compute the squared [absolute value][absolute-value] for each element in a strided array.
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<section class="intro">
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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 abs2 = require( '@stdlib/math/strided/special/abs2' );
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```
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#### abs2( N, x, strideX, y, strideY )
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Computes the squared [absolute value][absolute-value] for each element in `x` and assigns the results to elements in `y`.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
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// Compute the squared absolute values in-place:
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abs2( x.length, x, 1, x, 1 );
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// x => <Float64Array>[ 4.0, 1.0, 9.0, 25.0, 16.0, 0.0, 1.0, 9.0 ]
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```
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The function accepts the following arguments:
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- **N**: number of indexed elements.
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- **x**: input array-like object.
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- **strideX**: index increment for `x`.
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- **y**: output array-like object.
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- **strideY**: index increment for `y`.
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The `N` and `stride` parameters determine which elements in `x` and `y` are accessed at runtime. For example, to index every other value in `x` and the first `N` elements of `y` in reverse order,
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
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var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
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var N = floor( x.length / 2 );
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abs2( N, x, 2, y, -1 );
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// y => <Float64Array>[ 25.0, 9.0, 1.0, 0.0, 0.0, 0.0 ]
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```
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Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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// Initial arrays...
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var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
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var y0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
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// Create offset views...
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
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var N = floor( x0.length / 2 );
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abs2( N, x1, -2, y1, 1 );
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// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]
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```
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#### abs2.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
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Computes the squared [absolute value][absolute-value] for each element in `x` and assigns the result to an element in `y` using alternative indexing semantics.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] );
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var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );
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abs2.ndarray( x.length, x, 1, 0, y, 1, 0 );
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// y => <Float64Array>[ 1.0, 4.0, 9.0, 16.0, 25.0 ]
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```
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The function accepts the following additional arguments:
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- **offsetX**: starting index for `x`.
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- **offsetY**: starting index for `y`.
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While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offsetX` and `offsetY` parameters support indexing semantics based on starting indices. For example, to index every other value in `x` starting from the second value and to index the last `N` elements in `y`,
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
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var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
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var N = floor( x.length / 2 );
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abs2.ndarray( N, x, 2, 1, y, -1, y.length-1 );
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// y => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- For output strided arrays having an integer data type, be careful of overflow, as overflow can lead to unexpected results.
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</section>
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<!-- /.notes -->
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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 discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
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var filledarray = require( '@stdlib/array/filled' );
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var dtypes = require( '@stdlib/array/dtypes' );
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var gfillBy = require( '@stdlib/blas/ext/base/gfill-by' );
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var abs2 = require( '@stdlib/math/strided/special/abs2' );
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var dt;
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var x;
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var y;
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var i;
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dt = dtypes();
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for ( i = 0; i < dt.length; i++ ) {
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x = filledarray( 0.0, 10, dt[ i ] );
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gfillBy( x.length, x, 1, discreteUniform( -10, 10 ) );
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console.log( x );
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y = filledarray( 0.0, x.length, dt[ i ] );
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console.log( y );
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abs2.ndarray( x.length, x, 1, 0, y, -1, y.length-1 );
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console.log( y );
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console.log( '' );
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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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[absolute-value]: https://en.wikipedia.org/wiki/Absolute_value
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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</section>
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<!-- /.links -->
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