cosine.js (1386B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var abs = require( '@stdlib/math/base/special/abs' ); 24 var isnan = require( '@stdlib/assert/is-nan' ); 25 var FOURTH_PI = require( '@stdlib/constants/float64/fourth-pi' ); 26 var HALF_PI = require( '@stdlib/constants/float64/half-pi' ); 27 var cos = require( '@stdlib/math/base/special/cos' ); 28 29 30 // MAIN // 31 32 /** 33 * Computes the cosine kernel for a value. 34 * 35 * @private 36 * @param {number} u - value for which we wish to calculate the cosine kernel 37 * @returns {number} the value for the kernel at u 38 * 39 * @example 40 * var u = 5; 41 * var out = cosine( u ); 42 * // returns 0 43 */ 44 function cosine(u) { 45 if ( isnan( u ) ) { 46 return NaN; 47 } 48 if ( abs( u ) > 1.0 ) { 49 return 0.0; 50 } 51 return FOURTH_PI * cos( HALF_PI * u ); 52 } 53 54 55 // EXPORTS // 56 57 module.exports = cosine;