ndarray.js (1802B)
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 // MAIN // 22 23 /** 24 * Computes the variance of a double-precision floating-point strided array provided a known mean and using a one-pass textbook algorithm. 25 * 26 * @param {PositiveInteger} N - number of indexed elements 27 * @param {number} mean - mean 28 * @param {number} correction - degrees of freedom adjustment 29 * @param {Float64Array} x - input array 30 * @param {integer} stride - stride length 31 * @param {NonNegativeInteger} offset - starting index 32 * @returns {number} variance 33 * 34 * @example 35 * var Float64Array = require( '@stdlib/array/float64' ); 36 * var floor = require( '@stdlib/math/base/special/floor' ); 37 * 38 * var x = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] ); 39 * var N = floor( x.length / 2 ); 40 * 41 * var v = dvarmtk( N, 1.25, 1, x, 2, 1 ); 42 * // returns 6.25 43 */ 44 function dvarmtk( N, mean, correction, x, stride, offset ) { 45 var ix; 46 var M2; 47 var d; 48 var n; 49 var i; 50 51 n = N - correction; 52 if ( N <= 0 || n <= 0.0 ) { 53 return NaN; 54 } 55 if ( N === 1 || stride === 0 ) { 56 return 0.0; 57 } 58 ix = offset; 59 M2 = 0.0; 60 for ( i = 0; i < N; i++ ) { 61 d = x[ ix ] - mean; 62 M2 += d * d; 63 ix += stride; 64 } 65 return M2 / n; 66 } 67 68 69 // EXPORTS // 70 71 module.exports = dvarmtk;