statistic.js (1450B)
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 PINF = require( '@stdlib/constants/float64/pinf' ); 24 25 26 // MAIN // 27 28 /** 29 * Computes a chi-square test statistic. 30 * 31 * @private 32 * @param {NonNegativeInteger} N - number of indexed elements 33 * @param {Float64Array} x - observation frequencies 34 * @param {integer} strideX - `x` stride length 35 * @param {Float64Array} y - expected frequencies 36 * @param {integer} strideY - `y` stride length 37 * @returns {number} test statistic 38 */ 39 function testStatistic( N, x, strideX, y, strideY ) { 40 var stat; 41 var v1; 42 var v2; 43 var d; 44 var i; 45 46 stat = 0.0; 47 for ( i = 0; i < N; i++ ) { 48 v1 = x[ i*strideX ]; 49 v2 = y[ i*strideY ]; 50 if ( v2 === 0.0 ) { 51 if ( v1 === 0.0 ) { 52 continue; 53 } 54 return PINF; 55 } 56 d = v1 - v2; 57 stat += ( d * d ) / v2; 58 } 59 return stat; 60 } 61 62 63 // EXPORTS // 64 65 module.exports = testStatistic;