factory.js (1978B)
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 isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' ); 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var ln = require( '@stdlib/math/base/special/ln' ); 27 var NINF = require( '@stdlib/constants/float64/ninf' ); 28 29 30 // MAIN // 31 32 /** 33 * Returns a function for evaluating the logarithm of the probability mass function (PMF) for a geometric distribution with success probability `p`. 34 * 35 * @param {Probability} p - success probability 36 * @returns {Function} logPMF 37 * 38 * @example 39 * var logpmf = factory( 0.5 ); 40 * var y = logpmf( 3.0 ); 41 * // returns ~-2.773 42 * 43 * y = logpmf( 1.0 ); 44 * // returns ~-1.386 45 */ 46 function factory( p ) { 47 if ( 48 isnan( p ) || 49 p < 0.0 || 50 p > 1.0 51 ) { 52 return constantFunction( NaN ); 53 } 54 return logpmf; 55 56 /** 57 * Evaluates the logarithm of the probability mass function (PMF) for a geometric distribution. 58 * 59 * @private 60 * @param {number} x - input value 61 * @returns {NonPositiveNumber} evaluated logPMF 62 * 63 * @example 64 * var y = logpmf( 2.0 ); 65 * // returns <number> 66 */ 67 function logpmf( x ) { 68 var q; 69 if ( isnan( x ) ) { 70 return NaN; 71 } 72 if ( isNonNegativeInteger( x ) ) { 73 q = 1.0 - p; 74 return ln( p ) + (x * ln( q )); 75 } 76 return NINF; 77 } 78 } 79 80 81 // EXPORTS // 82 83 module.exports = factory;