gnrm2.js (1673B)
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 sqrt = require( '@stdlib/math/base/special/sqrt' ); 24 var abs = require( '@stdlib/math/base/special/abs' ); 25 var pow = require( '@stdlib/math/base/special/pow' ); 26 27 28 // MAIN // 29 30 /** 31 * Computes the L2-norm of a vector. 32 * 33 * @param {PositiveInteger} N - number of values over which to compute the L2-norm 34 * @param {NumericArray} x - input array 35 * @param {PositiveInteger} stride - stride length 36 * @returns {number} L2-norm 37 * 38 * @example 39 * var x = [ 1.0, -2.0, 2.0 ]; 40 * 41 * var z = gnrm2( x.length, x, 1 ); 42 * // returns 3.0 43 */ 44 function gnrm2( N, x, stride ) { 45 var scale; 46 var ssq; 47 var ax; 48 var i; 49 50 if ( N <= 0 || stride <= 0 ) { 51 return 0.0; 52 } 53 if ( N === 1 ) { 54 return abs( x[ 0 ] ); 55 } 56 scale = 0.0; 57 ssq = 1.0; 58 N *= stride; 59 for ( i = 0; i < N; i += stride ) { 60 if ( x[ i ] !== 0.0 ) { 61 ax = abs( x[ i ] ); 62 if ( scale < ax ) { 63 ssq = 1.0 + ( ssq * pow( scale/ax, 2 ) ); 64 scale = ax; 65 } else { 66 ssq += pow( ax/scale, 2 ); 67 } 68 } 69 } 70 return scale * sqrt( ssq ); 71 } 72 73 74 // EXPORTS // 75 76 module.exports = gnrm2;