README.md (6884B)
1 <!-- 2 3 @license Apache-2.0 4 5 Copyright (c) 2021 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 <!-- lint disable maximum-heading-length --> 22 23 # ahavercosBy 24 25 > Compute the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array via a callback function. 26 27 <section class="intro"> 28 29 </section> 30 31 <!-- /.intro --> 32 33 <section class="usage"> 34 35 ## Usage 36 37 ```javascript 38 var ahavercosBy = require( '@stdlib/math/strided/special/ahavercos-by' ); 39 ``` 40 41 #### ahavercosBy( N, x, strideX, y, strideY, clbk\[, thisArg] ) 42 43 Computes the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y`. 44 45 ```javascript 46 function accessor( v ) { 47 return v; 48 } 49 50 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ]; 51 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ]; 52 53 ahavercosBy( x.length, x, 1, y, 1, accessor ); 54 // y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ] 55 ``` 56 57 The function accepts the following arguments: 58 59 - **N**: number of indexed elements. 60 - **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions). 61 - **strideX**: index increment for `x`. 62 - **y**: output [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions). 63 - **strideY**: index increment for `y`. 64 - **clbk**: callback function. 65 - **thisArg**: execution context (_optional_). 66 67 The invoked callback function is provided six arguments: 68 69 - **value**: input array element. 70 - **idx**: iteration index (zero-based). 71 - **xi**: input array strided index (`offsetX + idx*strideX`). 72 - **yi**: output array strided index (`offsetY + idx*strideY`). 73 - **x**: input array/collection. 74 - **y**: output array/collection. 75 76 To set the callback execution context, provide a `thisArg`. 77 78 ```javascript 79 function accessor( v ) { 80 this.count += 1; 81 return v; 82 } 83 84 var context = { 85 'count': 0 86 }; 87 88 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ]; 89 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ]; 90 91 ahavercosBy( x.length, x, 1, y, 1, accessor, context ); 92 // y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ] 93 94 var cnt = context.count; 95 // returns 8 96 ``` 97 98 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 to index the first `N` elements of `y` in reverse order, 99 100 ```javascript 101 function accessor( v ) { 102 return v; 103 } 104 105 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ]; 106 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]; 107 108 ahavercosBy( 3, x, 2, y, -1, accessor ); 109 // y => [ ~1.047, 0.0, ~3.142, 0.0, 0.0, 0.0 ] 110 ``` 111 112 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. 113 114 ```javascript 115 var Float64Array = require( '@stdlib/array/float64' ); 116 117 function accessor( v ) { 118 return v; 119 } 120 121 // Initial arrays... 122 var x0 = new Float64Array( [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ] ); 123 var y0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] ); 124 125 // Create offset views... 126 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element 127 var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element 128 129 ahavercosBy( 3, x1, -2, y1, 1, accessor ); 130 // y0 => <Float64Array>[ 0.0, 0.0, 0.0, ~1.203, ~2.094, ~1.571 ] 131 ``` 132 133 #### ahavercosBy.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, clbk\[, thisArg] ) 134 135 Computes the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y` using alternative indexing semantics. 136 137 ```javascript 138 function accessor( v ) { 139 return v; 140 } 141 142 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ]; 143 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ]; 144 145 ahavercosBy.ndarray( x.length, x, 1, 0, y, 1, 0, accessor ); 146 // y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ] 147 ``` 148 149 The function accepts the following additional arguments: 150 151 - **offsetX**: starting index for `x`. 152 - **offsetY**: starting index for `y`. 153 154 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`, 155 156 ```javascript 157 function accessor( v ) { 158 return v; 159 } 160 161 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ]; 162 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]; 163 164 ahavercosBy.ndarray( 3, x, 2, 1, y, -1, y.length-1, accessor ); 165 // y => [ 0.0, 0.0, 0.0, ~1.203, ~2.094, ~1.571 ] 166 ``` 167 168 </section> 169 170 <!-- /.usage --> 171 172 <section class="notes"> 173 174 ## Notes 175 176 - If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**. 177 178 ```javascript 179 function accessor() { 180 // No-op... 181 } 182 183 var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ]; 184 var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ]; 185 186 ahavercosBy( x.length, x, 1, y, 1, accessor ); 187 // y => [ 0.0, 0.0, 0.0, 0.0, 0.0 ] 188 ``` 189 190 </section> 191 192 <!-- /.notes --> 193 194 <section class="examples"> 195 196 ## Examples 197 198 <!-- eslint no-undef: "error" --> 199 200 ```javascript 201 var uniform = require( '@stdlib/random/base/uniform' ); 202 var filledarray = require( '@stdlib/array/filled' ); 203 var ahavercosBy = require( '@stdlib/math/strided/special/ahavercos-by' ); 204 205 function accessor( v, i ) { 206 if ( (i%3) === 0 ) { 207 // Simulate a "missing" value... 208 return; 209 } 210 return v; 211 } 212 213 var x = filledarray( 0.0, 10, 'generic' ); 214 var y = filledarray( null, 10, 'generic' ); 215 216 var i; 217 for ( i = 0; i < x.length; i++ ) { 218 x[ i ] = uniform( 0.0, 1.0 ); 219 } 220 console.log( x ); 221 console.log( y ); 222 223 ahavercosBy.ndarray( x.length, x, 1, 0, y, -1, y.length-1, accessor ); 224 console.log( y ); 225 ``` 226 227 </section> 228 229 <!-- /.examples --> 230 231 <section class="links"> 232 233 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array 234 235 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 236 237 [@stdlib/math/base/special/ahavercos]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/ahavercos 238 239 </section> 240 241 <!-- /.links -->