77 lines
1.6 KiB
JavaScript
77 lines
1.6 KiB
JavaScript
|
/**
|
||
|
|
* @license Apache-2.0
|
||
|
|
*
|
||
|
|
* Copyright (c) 2020 The Stdlib Authors.
|
||
|
|
*
|
||
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
||
|
|
* you may not use this file except in compliance with the License.
|
||
|
|
* You may obtain a copy of the License at
|
||
|
|
*
|
||
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
||
|
|
*
|
||
|
|
* Unless required by applicable law or agreed to in writing, software
|
||
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
||
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||
|
|
* See the License for the specific language governing permissions and
|
||
|
|
* limitations under the License.
|
||
|
|
*/
|
||
|
|
|
||
|
|
'use strict';
|
||
|
|
|
||
|
|
// MODULES //
|
||
|
|
|
||
|
|
var sqrt = require( '@stdlib/math/base/special/sqrt' );
|
||
|
|
var abs = require( '@stdlib/math/base/special/abs' );
|
||
|
|
var pow = require( '@stdlib/math/base/special/pow' );
|
||
|
|
|
||
|
|
|
||
|
|
// MAIN //
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Computes the L2-norm of a vector.
|
||
|
|
*
|
||
|
|
* @param {PositiveInteger} N - number of values over which to compute the L2-norm
|
||
|
|
* @param {NumericArray} x - input array
|
||
|
|
* @param {PositiveInteger} stride - stride length
|
||
|
|
* @returns {number} L2-norm
|
||
|
|
*
|
||
|
|
* @example
|
||
|
|
* var x = [ 1.0, -2.0, 2.0 ];
|
||
|
|
*
|
||
|
|
* var z = gnrm2( x.length, x, 1 );
|
||
|
|
* // returns 3.0
|
||
|
|
*/
|
||
|
|
function gnrm2( N, x, stride ) {
|
||
|
|
var scale;
|
||
|
|
var ssq;
|
||
|
|
var ax;
|
||
|
|
var i;
|
||
|
|
|
||
|
|
if ( N <= 0 || stride <= 0 ) {
|
||
|
|
return 0.0;
|
||
|
|
}
|
||
|
|
if ( N === 1 ) {
|
||
|
|
return abs( x[ 0 ] );
|
||
|
|
}
|
||
|
|
scale = 0.0;
|
||
|
|
ssq = 1.0;
|
||
|
|
N *= stride;
|
||
|
|
for ( i = 0; i < N; i += stride ) {
|
||
|
|
if ( x[ i ] !== 0.0 ) {
|
||
|
|
ax = abs( x[ i ] );
|
||
|
|
if ( scale < ax ) {
|
||
|
|
ssq = 1.0 + ( ssq * pow( scale/ax, 2 ) );
|
||
|
|
scale = ax;
|
||
|
|
} else {
|
||
|
|
ssq += pow( ax/scale, 2 );
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return scale * sqrt( ssq );
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
// EXPORTS //
|
||
|
|
|
||
|
|
module.exports = gnrm2;
|