factory.js (1793B)
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( './../../../../base/assert/is-nan' ); 25 var isint = require( './../../../../base/assert/is-integer' ); 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating a normalized Hermite polynomial. 32 * 33 * @param {NonNegativeInteger} n - polynomial degree 34 * @returns {Function} function for evaluating a normalized Hermite polynomial 35 * 36 * @example 37 * var polyval = factory( 2 ); 38 * 39 * var v = polyval( 0.5 ); 40 * // returns -0.75 41 */ 42 function factory( n ) { 43 if ( n < 0 || isnan( n ) || !isint( n ) ) { 44 return constantFunction( NaN ); 45 } 46 if ( n === 0 ) { 47 return constantFunction( 1.0 ); 48 } 49 return polyval; 50 51 /** 52 * Evaluates a normalized Hermite polynomial. 53 * 54 * @private 55 * @param {number} x - value at which to evaluate a normalized Hermite polynomial 56 * @returns {number} result 57 */ 58 function polyval( x ) { 59 var y1; 60 var y2; 61 var y3; 62 var i; 63 64 if ( isnan( x ) ) { 65 return NaN; 66 } 67 y2 = 1.0; 68 y3 = 0.0; 69 for ( i = n; i > 1; i-- ) { 70 y1 = (x*y2) - (i*y3); 71 y3 = y2; 72 y2 = y1; 73 } 74 return (x*y2) - y3; 75 } 76 } 77 78 79 // EXPORTS // 80 81 module.exports = factory;