ndarray.js (2137B)
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 var sapxsumpw = require( '@stdlib/blas/ext/base/sapxsumpw' ).ndarray; 25 26 27 // MAIN // 28 29 /** 30 * Computes the arithmetic mean of a single-precision floating-point strided array using a one-pass trial mean algorithm with pairwise summation. 31 * 32 * ## References 33 * 34 * - Ling, Robert F. 1974. "Comparison of Several Algorithms for Computing Sample Means and Variances." _Journal of the American Statistical Association_ 69 (348). American Statistical Association, Taylor & Francis, Ltd.: 859–66. doi:[10.2307/2286154](https://doi.org/10.2307/2286154). 35 * 36 * @param {PositiveInteger} N - number of indexed elements 37 * @param {Float32Array} x - input array 38 * @param {integer} stride - stride length 39 * @param {NonNegativeInteger} offset - starting index 40 * @returns {number} arithmetic mean 41 * 42 * @example 43 * var Float32Array = require( '@stdlib/array/float32' ); 44 * var floor = require( '@stdlib/math/base/special/floor' ); 45 * 46 * var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] ); 47 * var N = floor( x.length / 2 ); 48 * 49 * var v = smeanlipw( N, x, 2, 1 ); 50 * // returns 1.25 51 */ 52 function smeanlipw( N, x, stride, offset ) { 53 if ( N <= 0 ) { 54 return NaN; 55 } 56 if ( N === 1 || stride === 0 ) { 57 return x[ offset ]; 58 } 59 return float64ToFloat32( x[ offset ] + float64ToFloat32( sapxsumpw( N-1, -x[ offset ], x, stride, offset+stride ) / N ) ); // eslint-disable-line max-len 60 } 61 62 63 // EXPORTS // 64 65 module.exports = smeanlipw;