evalpoly.js (1456B)
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 // MAIN // 22 23 /** 24 * Evaluates a polynomial. 25 * 26 * ## Notes 27 * 28 * - The implementation uses [Horner's rule][horners-method] for efficient computation. 29 * 30 * [horners-method]: https://en.wikipedia.org/wiki/Horner%27s_method 31 * 32 * 33 * @param {NumericArray} c - polynomial coefficients sorted in ascending degree 34 * @param {number} x - value at which to evaluate the polynomial 35 * @returns {number} evaluated polynomial 36 * 37 * @example 38 * var v = evalpoly( [3.0,2.0,1.0], 10.0 ); // 3*10^0 + 2*10^1 + 1*10^2 39 * // returns 123.0 40 */ 41 function evalpoly( c, x ) { 42 var p; 43 var i; 44 45 i = c.length; 46 if ( i < 2 || x === 0.0 ) { 47 if ( i === 0 ) { 48 return 0.0; 49 } 50 return c[ 0 ]; 51 } 52 i -= 1; 53 p = ( c[ i ] * x ) + c[ i-1 ]; 54 i -= 2; 55 while ( i >= 0 ) { 56 p = ( p * x ) + c[ i ]; 57 i -= 1; 58 } 59 return p; 60 } 61 62 63 // EXPORTS // 64 65 module.exports = evalpoly;