factory.js (1956B)
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 constantFunction = require( '@stdlib/utils/constant-function' ); 24 var degenerate = require( './../../../../../base/dists/degenerate/pdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var cospi = require( '@stdlib/math/base/special/cospi' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the probability density function (PDF) for a raised cosine distribution. 33 * 34 * @param {number} mu - location parameter 35 * @param {NonNegativeNumber} s - scale parameter 36 * @returns {Function} PDF 37 * 38 * @example 39 * var pdf = factory( 0.0, 3.0 ); 40 * var y = pdf( 2.0 ); 41 * // returns ~0.083 42 * 43 * y = pdf( 5.0 ); 44 * // returns 0.0 45 */ 46 function factory( mu, s ) { 47 if ( isnan( mu ) || isnan( s ) || s < 0.0 ) { 48 return constantFunction( NaN ); 49 } 50 if ( s === 0.0 ) { 51 return degenerate( mu ); 52 } 53 return pdf; 54 55 /** 56 * Evaluates the probability density function (PDF) for a raised cosine distribution. 57 * 58 * @private 59 * @param {number} x - input value 60 * @returns {number} evaluated PDF 61 * 62 * @example 63 * var y = pdf( -1.2 ); 64 * // returns <number> 65 */ 66 function pdf( x ) { 67 var z; 68 if ( isnan( x ) ) { 69 return NaN; 70 } 71 if ( 72 x < mu - s || 73 x > mu + s 74 ) { 75 return 0.0; 76 } 77 z = ( x - mu ) / s; 78 return ( 1.0 + cospi( z ) ) / ( 2.0 * s ); 79 } 80 } 81 82 83 // EXPORTS // 84 85 module.exports = factory;