factory.js (2080B)
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 isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 var log1p = require( '@stdlib/math/base/special/log1p' ); 26 var ceil = require( '@stdlib/math/base/special/ceil' ); 27 var max = require( '@stdlib/math/base/special/max' ); 28 var ln = require( '@stdlib/math/base/special/ln' ); 29 var PINF = require( '@stdlib/constants/float64/pinf' ); 30 31 32 // MAIN // 33 34 /** 35 * Returns a function for evaluating the quantile function for a geometric distribution with success probability `p`. 36 * 37 * @param {Probability} p - success probability 38 * @returns {Function} quantile function 39 * 40 * @example 41 * var quantile = factory( 0.4 ); 42 * var y = quantile( 0.4 ); 43 * // returns 0 44 * 45 * y = quantile( 0.8 ); 46 * // returns 3 47 * 48 * y = quantile( 1.0 ); 49 * // returns Infinity 50 */ 51 function factory( p ) { 52 if ( isnan( p ) || p < 0.0 || p > 1.0 ) { 53 return constantFunction( NaN ); 54 } 55 return quantile; 56 57 /** 58 * Evaluates the quantile function for a geometric distribution. 59 * 60 * @private 61 * @param {Probability} r - input value 62 * @returns {NonNegativeInteger} evaluated quantile function 63 * 64 * @example 65 * var y = quantile( 0.3 ); 66 * // returns <number> 67 */ 68 function quantile( r ) { 69 if ( isnan( r ) || r < 0.0 || r > 1.0 ) { 70 return NaN; 71 } 72 if ( r === 1.0 ) { 73 return PINF; 74 } 75 return max( 0.0, ceil( (ln(1.0-r) / log1p(-p)) - (1.0 + 1e-12) ) ); 76 } 77 } 78 79 80 // EXPORTS // 81 82 module.exports = factory;