173 lines
4.4 KiB
Markdown
173 lines
4.4 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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# dapx
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> Add a constant to each element in a double-precision floating-point strided array.
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<section class="usage">
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## Usage
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```javascript
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var dapx = require( '@stdlib/blas/ext/base/dapx' );
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```
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#### dapx( N, alpha, x, stride )
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Adds a constant `alpha` to each element in a double-precision floating-point strided array `x`.
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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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dapx( x.length, 5.0, x, 1 );
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// x => <Float64Array>[ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]
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```
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The function has the following parameters:
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- **N**: number of indexed elements.
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- **alpha**: scalar constant.
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- **x**: input [`Float64Array`][@stdlib/array/float64].
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- **stride**: index increment.
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The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to add a constant to every other element
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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( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
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var N = floor( x.length / 2 );
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dapx( N, 5.0, x, 2 );
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// x => <Float64Array>[ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -3.0 ]
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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 array...
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var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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// Create an offset view...
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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var N = floor( x0.length/2 );
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// Add a constant to every other element...
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dapx( N, 5.0, x1, 2 );
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// x0 => <Float64Array>[ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]
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```
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#### dapx.ndarray( N, alpha, x, stride, offset )
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Adds a constant `alpha` to each element in a double-precision floating-point strided array `x` 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( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
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dapx.ndarray( x.length, 5.0, x, 1, 0 );
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// x => <Float64Array>[ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]
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```
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The function has the following additional parameters:
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- **offset**: starting index.
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While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to access only the last three elements of `x`
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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, -6.0 ] );
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dapx.ndarray( 3, 5.0, x, 1, x.length-3 );
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// x => <Float64Array>[ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]
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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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- If `N <= 0`, both functions return `x` unchanged.
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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 round = require( '@stdlib/math/base/special/round' );
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var randu = require( '@stdlib/random/base/randu' );
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var Float64Array = require( '@stdlib/array/float64' );
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var dapx = require( '@stdlib/blas/ext/base/dapx' );
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var rand;
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var sign;
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var x;
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var i;
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x = new Float64Array( 10 );
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for ( i = 0; i < x.length; i++ ) {
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rand = round( randu()*100.0 );
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sign = randu();
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if ( sign < 0.5 ) {
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sign = -1.0;
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} else {
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sign = 1.0;
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}
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x[ i ] = sign * rand;
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}
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console.log( x );
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dapx( x.length, 5.0, x, 1 );
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console.log( x );
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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/array/float64]: https://www.npmjs.com/package/@stdlib/array-float64
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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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