triweight.js (1289B)
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 pow = require( '@stdlib/math/base/special/pow' ); 26 27 28 // MAIN // 29 30 /** 31 * Computes the Triweight kernel for a value. 32 * 33 * @private 34 * @param {number} u - value for which we wish to calculate the Triweight kernel 35 * @returns {number} the value for the kernel at u 36 * 37 * @example 38 * var u = 5; 39 * out = triweight(u); // returns 0 40 */ 41 function triweight(u) { 42 var absU; 43 44 if (isnan(u)) { 45 return NaN; 46 } 47 48 absU = abs(u); 49 if (absU > 1) { 50 return 0; 51 } 52 return (35 / 32) * pow(1.0 - pow(u, 2.0), 3.0); 53 } 54 55 56 // EXPORTS // 57 58 module.exports = triweight;