README.md (5063B)
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 # cumaxabs 22 23 > Calculate the cumulative maximum absolute value of 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 cumaxabs = require( '@stdlib/stats/base/cumaxabs' ); 37 ``` 38 39 #### cumaxabs( N, x, strideX, y, strideY ) 40 41 Computes the cumulative maximum absolute value of a strided array. 42 43 ```javascript 44 var x = [ 1.0, -2.0, 2.0 ]; 45 var y = [ 0.0, 0.0, 0.0 ]; 46 47 cumaxabs( x.length, x, 1, y, 1 ); 48 // y => [ 1.0, 2.0, 2.0 ] 49 ``` 50 51 The function has the following parameters: 52 53 - **N**: number of indexed elements. 54 - **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array]. 55 - **strideX**: index increment for `x`. 56 - **y**: output [`Array`][mdn-array] or [`typed array`][mdn-typed-array]. 57 - **strideY**: index increment for `y`. 58 59 The `N` and `stride` parameters determine which elements in `x` and `y` are accessed at runtime. For example, to compute the cumulative maximum absolute value of every other element in `x`, 60 61 ```javascript 62 var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ]; 63 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]; 64 65 var v = cumaxabs( 4, x, 2, y, 1 ); 66 // y => [ 1.0, 2.0, 2.0, 4.0, 0.0, 0.0, 0.0, 0.0 ] 67 ``` 68 69 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. 70 71 <!-- eslint-disable stdlib/capitalized-comments --> 72 73 ```javascript 74 var Float64Array = require( '@stdlib/array/float64' ); 75 76 // Initial arrays... 77 var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] ); 78 var y0 = new Float64Array( x0.length ); 79 80 // Create offset views... 81 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element 82 var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element 83 84 cumaxabs( 4, x1, -2, y1, 1 ); 85 // y0 => <Float64Array>[ 0.0, 0.0, 0.0, 4.0, 4.0, 4.0, 4.0, 0.0 ] 86 ``` 87 88 #### cumaxabs.ndarray( N, x, strideX, offsetX, y, strideY, offsetY ) 89 90 Computes the cumulative maximum absolute value of a strided array using alternative indexing semantics. 91 92 ```javascript 93 var x = [ 1.0, -2.0, 2.0 ]; 94 var y = [ 0.0, 0.0, 0.0 ]; 95 96 cumaxabs.ndarray( x.length, x, 1, 0, y, 1, 0 ); 97 // y => [ 1.0, 2.0, 2.0 ] 98 ``` 99 100 The function has the following additional parameters: 101 102 - **offsetX**: starting index for `x`. 103 - **offsetY**: starting index for `y`. 104 105 While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, `offsetX` and `offsetY` parameters support indexing semantics based on a starting indices. For example, to calculate the cumulative maximum absolute value of every other value in `x` starting from the second value and to store in the last `N` elements of `y` starting from the last element 106 107 ```javascript 108 var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ]; 109 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]; 110 111 cumaxabs.ndarray( 4, x, 2, 1, y, -1, y.length-1 ); 112 // y => [ 0.0, 0.0, 0.0, 0.0, 4.0, 2.0, 2.0, 1.0 ] 113 ``` 114 115 </section> 116 117 <!-- /.usage --> 118 119 <section class="notes"> 120 121 ## Notes 122 123 - If `N <= 0`, both functions return `y` unchanged. 124 - Depending on the environment, the typed versions ([`dcumaxabs`][@stdlib/stats/base/dcumaxabs], [`scumaxabs`][@stdlib/stats/base/scumaxabs], etc.) are likely to be significantly more performant. 125 126 </section> 127 128 <!-- /.notes --> 129 130 <section class="examples"> 131 132 ## Examples 133 134 <!-- eslint no-undef: "error" --> 135 136 ```javascript 137 var randu = require( '@stdlib/random/base/randu' ); 138 var round = require( '@stdlib/math/base/special/round' ); 139 var Float64Array = require( '@stdlib/array/float64' ); 140 var cumaxabs = require( '@stdlib/stats/base/cumaxabs' ); 141 142 var y; 143 var x; 144 var i; 145 146 x = new Float64Array( 10 ); 147 y = new Float64Array( x.length ); 148 for ( i = 0; i < x.length; i++ ) { 149 x[ i ] = round( randu()*100.0 ); 150 } 151 console.log( x ); 152 console.log( y ); 153 154 cumaxabs( x.length, x, 1, y, -1 ); 155 console.log( y ); 156 ``` 157 158 </section> 159 160 <!-- /.examples --> 161 162 <section class="references"> 163 164 </section> 165 166 <!-- /.references --> 167 168 <section class="links"> 169 170 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array 171 172 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 173 174 [@stdlib/stats/base/dcumaxabs]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/dcumaxabs 175 176 [@stdlib/stats/base/scumaxabs]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/scumaxabs 177 178 </section> 179 180 <!-- /.links -->