ndarray.js (2036B)
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 float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' ); 24 25 26 // MAIN // 27 28 /** 29 * Computes the variance of a single-precision floating-point strided array using a one-pass textbook algorithm. 30 * 31 * @param {PositiveInteger} N - number of indexed elements 32 * @param {number} correction - degrees of freedom adjustment 33 * @param {Float32Array} x - input array 34 * @param {integer} stride - stride length 35 * @param {NonNegativeInteger} offset - starting index 36 * @returns {number} variance 37 * 38 * @example 39 * var Float32Array = require( '@stdlib/array/float32' ); 40 * var floor = require( '@stdlib/math/base/special/floor' ); 41 * 42 * var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] ); 43 * var N = floor( x.length / 2 ); 44 * 45 * var v = svariancetk( N, 1, x, 2, 1 ); 46 * // returns 6.25 47 */ 48 function svariancetk( N, correction, x, stride, offset ) { 49 var S2; 50 var ix; 51 var S; 52 var v; 53 var n; 54 var i; 55 56 n = N - correction; 57 if ( N <= 0 || n <= 0.0 ) { 58 return NaN; 59 } 60 if ( N === 1 || stride === 0 ) { 61 return 0.0; 62 } 63 ix = offset; 64 S2 = 0.0; 65 S = 0.0; 66 for ( i = 0; i < N; i++ ) { 67 v = x[ ix ]; 68 S2 = float64ToFloat32( S2 + float64ToFloat32( v*v ) ); 69 S = float64ToFloat32( S+v ); 70 ix += stride; 71 } 72 return float64ToFloat32( float64ToFloat32(S2 - float64ToFloat32(float64ToFloat32(S/N)*S)) / n ); // eslint-disable-line max-len 73 } 74 75 76 // EXPORTS // 77 78 module.exports = svariancetk;