dnrm2.js (1797B)
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 double-precision floating-point vector. 32 * 33 * @param {PositiveInteger} N - number of values over which to compute the L2-norm 34 * @param {Float64Array} x - input array 35 * @param {PositiveInteger} stride - stride length 36 * @returns {number} L2-norm of `x` 37 * 38 * @example 39 * var Float64Array = require( '@stdlib/array/float64' ); 40 * 41 * var x = new Float64Array( [ 1.0, -2.0, 2.0 ] ); 42 * var N = 3; 43 * 44 * var z = dnrm2( N, x, 1 ); 45 * // returns 3.0 46 */ 47 function dnrm2( N, x, stride ) { 48 var scale; 49 var ssq; 50 var ax; 51 var i; 52 53 if ( N <= 0 || stride <= 0 ) { 54 return 0.0; 55 } 56 if ( N === 1 ) { 57 return abs( x[ 0 ] ); 58 } 59 scale = 0.0; 60 ssq = 1.0; 61 N *= stride; 62 for ( i = 0; i < N; i += stride ) { 63 if ( x[ i ] !== 0.0 ) { 64 ax = abs( x[ i ] ); 65 if ( scale < ax ) { 66 ssq = 1.0 + ( ssq * pow( scale/ax, 2 ) ); 67 scale = ax; 68 } else { 69 ssq += pow( ax/scale, 2 ); 70 } 71 } 72 } 73 return scale * sqrt( ssq ); 74 } 75 76 77 // EXPORTS // 78 79 module.exports = dnrm2;