weights.js (1308B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2020 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 memoize = require( '@stdlib/utils/memoize' ); 24 25 26 // VARIABLES // 27 28 var memoized; 29 30 31 // FUNCTIONS // 32 33 /** 34 * Calculates the weight for the `(x,n)` pair and memoizes the result. 35 * 36 * @private 37 * @param {number} x - input value 38 * @param {NonNegativeInteger} n - number of observations 39 * @returns {number} weight 40 */ 41 function weights( x, n ) { 42 var mlim; 43 44 if ( n === 0 ) { 45 return ( x === 0 ) ? 1 : 0; 46 } 47 mlim = n * ( n + 1 ) / 2; 48 if ( x < 0 || x > mlim ) { 49 return 0; 50 } 51 if ( x > mlim / 2 ) { 52 x = mlim - x; 53 } 54 return memoized( x - n, n - 1 ) + memoized( x, n - 1 ); 55 } 56 57 58 // MAIN // 59 60 memoized = memoize( weights ); 61 62 63 // EXPORTS // 64 65 module.exports = memoized;