README.md (5506B)
1 <!-- 2 3 @license Apache-2.0 4 5 Copyright (c) 2020 The Stdlib Authors. 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 19 --> 20 21 # abs2 22 23 > Compute the squared [absolute value][absolute-value] for each element in a strided array. 24 25 <section class="intro"> 26 27 </section> 28 29 <!-- /.intro --> 30 31 <section class="usage"> 32 33 ## Usage 34 35 ```javascript 36 var abs2 = require( '@stdlib/math/strided/special/abs2' ); 37 ``` 38 39 #### abs2( N, x, strideX, y, strideY ) 40 41 Computes the squared [absolute value][absolute-value] for each element in `x` and assigns the results to elements in `y`. 42 43 ```javascript 44 var Float64Array = require( '@stdlib/array/float64' ); 45 46 var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] ); 47 48 // Compute the squared absolute values in-place: 49 abs2( x.length, x, 1, x, 1 ); 50 // x => <Float64Array>[ 4.0, 1.0, 9.0, 25.0, 16.0, 0.0, 1.0, 9.0 ] 51 ``` 52 53 The function accepts the following arguments: 54 55 - **N**: number of indexed elements. 56 - **x**: input array-like object. 57 - **strideX**: index increment for `x`. 58 - **y**: output array-like object. 59 - **strideY**: index increment for `y`. 60 61 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, 62 63 ```javascript 64 var Float64Array = require( '@stdlib/array/float64' ); 65 var floor = require( '@stdlib/math/base/special/floor' ); 66 67 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 68 var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] ); 69 70 var N = floor( x.length / 2 ); 71 72 abs2( N, x, 2, y, -1 ); 73 // y => <Float64Array>[ 25.0, 9.0, 1.0, 0.0, 0.0, 0.0 ] 74 ``` 75 76 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. 77 78 ```javascript 79 var Float64Array = require( '@stdlib/array/float64' ); 80 var floor = require( '@stdlib/math/base/special/floor' ); 81 82 // Initial arrays... 83 var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 84 var y0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] ); 85 86 // Create offset views... 87 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element 88 var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element 89 90 var N = floor( x0.length / 2 ); 91 92 abs2( N, x1, -2, y1, 1 ); 93 // y0 => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ] 94 ``` 95 96 #### abs2.ndarray( N, x, strideX, offsetX, y, strideY, offsetY ) 97 98 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. 99 100 ```javascript 101 var Float64Array = require( '@stdlib/array/float64' ); 102 103 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] ); 104 var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] ); 105 106 abs2.ndarray( x.length, x, 1, 0, y, 1, 0 ); 107 // y => <Float64Array>[ 1.0, 4.0, 9.0, 16.0, 25.0 ] 108 ``` 109 110 The function accepts the following additional arguments: 111 112 - **offsetX**: starting index for `x`. 113 - **offsetY**: starting index for `y`. 114 115 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`, 116 117 ```javascript 118 var Float64Array = require( '@stdlib/array/float64' ); 119 var floor = require( '@stdlib/math/base/special/floor' ); 120 121 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 122 var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] ); 123 124 var N = floor( x.length / 2 ); 125 126 abs2.ndarray( N, x, 2, 1, y, -1, y.length-1 ); 127 // y => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ] 128 ``` 129 130 </section> 131 132 <!-- /.usage --> 133 134 <section class="notes"> 135 136 ## Notes 137 138 - For output strided arrays having an integer data type, be careful of overflow, as overflow can lead to unexpected results. 139 140 </section> 141 142 <!-- /.notes --> 143 144 <section class="examples"> 145 146 ## Examples 147 148 <!-- eslint no-undef: "error" --> 149 150 ```javascript 151 var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory; 152 var filledarray = require( '@stdlib/array/filled' ); 153 var dtypes = require( '@stdlib/array/dtypes' ); 154 var gfillBy = require( '@stdlib/blas/ext/base/gfill-by' ); 155 var abs2 = require( '@stdlib/math/strided/special/abs2' ); 156 157 var dt; 158 var x; 159 var y; 160 var i; 161 162 dt = dtypes(); 163 for ( i = 0; i < dt.length; i++ ) { 164 x = filledarray( 0.0, 10, dt[ i ] ); 165 gfillBy( x.length, x, 1, discreteUniform( -10, 10 ) ); 166 console.log( x ); 167 168 y = filledarray( 0.0, x.length, dt[ i ] ); 169 console.log( y ); 170 171 abs2.ndarray( x.length, x, 1, 0, y, -1, y.length-1 ); 172 console.log( y ); 173 console.log( '' ); 174 } 175 ``` 176 177 </section> 178 179 <!-- /.examples --> 180 181 <section class="links"> 182 183 [absolute-value]: https://en.wikipedia.org/wiki/Absolute_value 184 185 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 186 187 </section> 188 189 <!-- /.links -->