ibeta_derivative.js (1305B)
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 ibetaPowerTerms = require( './ibeta_power_terms.js' ); 24 25 26 // MAIN // 27 28 /** 29 * Computes the partial derivative with respect to x of the incomplete beta function. 30 * 31 * @private 32 * @param {Probability} x - input value (0 < x <= 1) 33 * @param {PositiveNumber} a - first parameter 34 * @param {PositiveNumber} b - second parameter (must be greater than 1) 35 * @returns {number} value of the partial derivative 36 */ 37 function ibetaDerivative( x, a, b ) { 38 var f1; 39 var y; 40 if ( x === 1.0 ) { 41 return 0.0; 42 } 43 // Regular cases: 44 f1 = ibetaPowerTerms( a, b, x, 1.0 - x, true ); 45 y = ( 1.0 - x ) * x; 46 f1 /= y; 47 return f1; 48 } 49 50 51 // EXPORTS // 52 53 module.exports = ibetaDerivative;