factory.js (2137B)
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/logpdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var cospi = require( '@stdlib/math/base/special/cospi' ); 27 var ln = require( '@stdlib/math/base/special/ln' ); 28 var NINF = require( '@stdlib/constants/float64/ninf' ); 29 30 31 // MAIN // 32 33 /** 34 * Returns a function for evaluating the logarithm of the probability density function (PDF) for a raised cosine distribution. 35 * 36 * @param {number} mu - location parameter 37 * @param {NonNegativeNumber} s - scale parameter 38 * @returns {Function} logPDF 39 * 40 * @example 41 * var logpdf = factory( 10.0, 2.0 ); 42 * var y = logpdf( 10.0 ); 43 * // returns ~-0.693 44 * 45 * y = logpdf( 9.0 ); 46 * // returns ~-1.386 47 */ 48 function factory( mu, s ) { 49 if ( isnan( mu ) || isnan( s ) || s < 0.0 ) { 50 return constantFunction( NaN ); 51 } 52 if ( s === 0.0 ) { 53 return degenerate( mu ); 54 } 55 return logpdf; 56 57 /** 58 * Evaluates the logarithm of the probability density function (PDF) for a raised cosine distribution. 59 * 60 * @private 61 * @param {number} x - input value 62 * @returns {number} evaluated logPDF 63 * 64 * @example 65 * var y = logpdf( -1.2 ); 66 * // returns <number> 67 */ 68 function logpdf( x ) { 69 var z; 70 if ( isnan( x ) ) { 71 return NaN; 72 } 73 if ( 74 x < mu - s || 75 x > mu + s 76 ) { 77 return NINF; 78 } 79 z = ( x - mu ) / s; 80 return ln( 1.0 + cospi( z ) ) - ln( 2.0 * s ); 81 } 82 } 83 84 85 // EXPORTS // 86 87 module.exports = factory;