time-to-botec

Benchmark sampling in different programming languages
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ndarray.js (2242B)

      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 ignoring `NaN` values and 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, NaN, NaN ] );
     43 * var N = floor( x.length / 2 );
     44 *
     45 * var v = snanvariancetk( N, 1, x, 2, 1 );
     46 * // returns 6.25
     47 */
     48 function snanvariancetk( N, correction, x, stride, offset ) {
     49 	var S2;
     50 	var ix;
     51 	var nc;
     52 	var S;
     53 	var v;
     54 	var n;
     55 	var i;
     56 
     57 	if ( N <= 0 ) {
     58 		return NaN;
     59 	}
     60 	if ( N === 1 || stride === 0 ) {
     61 		v = x[ offset ];
     62 		if ( v === v && N-correction > 0.0 ) {
     63 			return 0.0;
     64 		}
     65 		return NaN;
     66 	}
     67 	ix = offset;
     68 	S2 = 0.0;
     69 	S = 0.0;
     70 	n = 0;
     71 	for ( i = 0; i < N; i++ ) {
     72 		v = x[ ix ];
     73 		if ( v === v ) {
     74 			S2 = float64ToFloat32( S2 + float64ToFloat32( v*v ) );
     75 			S = float64ToFloat32( S + v );
     76 			n += 1;
     77 		}
     78 		ix += stride;
     79 	}
     80 	nc = n - correction;
     81 	if ( nc <= 0.0 ) {
     82 		return NaN;
     83 	}
     84 	return float64ToFloat32( float64ToFloat32(S2 - float64ToFloat32(float64ToFloat32(S/n)*S)) / nc ); // eslint-disable-line max-len
     85 }
     86 
     87 
     88 // EXPORTS //
     89 
     90 module.exports = snanvariancetk;