factory.js (2289B)
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/logcdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var sinpi = require( '@stdlib/math/base/special/sinpi' ); 27 var ln = require( '@stdlib/math/base/special/ln' ); 28 var NINF = require( '@stdlib/constants/float64/ninf' ); 29 var PI = require( '@stdlib/constants/float64/pi' ); 30 31 32 // MAIN // 33 34 /** 35 * Returns a function for evaluating the natural logarithm of the cumulative distribution function (CDF) for a raised cosine distribution with location parameter `mu` and scale parameter `s`. 36 * 37 * @param {number} mu - location parameter 38 * @param {NonNegativeNumber} s - scale parameter 39 * @returns {Function} logCDF 40 * 41 * @example 42 * var logcdf = factory( 3.0, 1.5 ); 43 * 44 * var y = logcdf( 1.9 ); 45 * // returns ~-4.2 46 * 47 * y = logcdf( 4.0 ); 48 * // returns ~-0.029 49 */ 50 function factory( mu, s ) { 51 if ( isnan( mu ) || isnan( s ) || s < 0.0 ) { 52 return constantFunction( NaN ); 53 } 54 if ( s === 0.0 ) { 55 return degenerate( mu ); 56 } 57 return logcdf; 58 59 /** 60 * Evaluates the natural logarithm of the cumulative distribution function (CDF) for a raised cosine distribution. 61 * 62 * @private 63 * @param {number} x - input value 64 * @returns {number} evaluated logCDF 65 * 66 * @example 67 * var y = logcdf( 2.0 ); 68 * // returns <number> 69 */ 70 function logcdf( x ) { 71 var z; 72 if ( isnan( x ) ) { 73 return NaN; 74 } 75 if ( x < mu - s ) { 76 return NINF; 77 } 78 if ( x > mu + s ) { 79 return 0.0; 80 } 81 z = ( x - mu ) / s; 82 return ln( ( 1.0 + z + ( sinpi( z ) / PI ) ) / 2.0 ); 83 } 84 } 85 86 87 // EXPORTS // 88 89 module.exports = factory;