Press n or j to go to the next uncovered block, b, p or k for the previous block.
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* @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 arraylike2object = require( '@stdlib/array/base/arraylike2object' );
var sqrt = require( '@stdlib/math/base/special/sqrt' );
var abs = require( '@stdlib/math/base/special/abs' );
var pow = require( '@stdlib/math/base/special/pow' );
var accessors = require( './accessors.js' );
// MAIN //
/**
* Computes the L2-norm of a vector.
*
* @param {PositiveInteger} N - number of indexed elements
* @param {NumericArray} x - input array
* @param {integer} stride - stride length
* @param {NonNegativeInteger} offset - starting index
* @returns {number} L2-norm
*
* @example
* var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ];
*
* var z = gnrm2( 4, x, 2, 1 );
* // returns 5.0
*/
function gnrm2( N, x, stride, offset ) {
var scale;
var ssq;
var ax;
var ix;
var o;
var i;
if ( N <= 0 ) {
return 0.0;
}
o = arraylike2object( x );
if ( o.accessorProtocol ) {
return accessors( N, o, stride, offset );
}
ix = offset;
if ( N === 1 ) {
return abs( x[ ix ] );
}
if ( stride === 0 ) {
return sqrt( N ) * abs( x[ ix ] );
}
scale = 0.0;
ssq = 1.0;
for ( i = 0; i < N; i++ ) {
if ( x[ ix ] !== 0.0 ) {
ax = abs( x[ ix ] );
if ( scale < ax ) {
ssq = 1.0 + ( ssq * pow( scale/ax, 2 ) );
scale = ax;
} else {
ssq += pow( ax/scale, 2 );
}
}
ix += stride;
}
return scale * sqrt( ssq );
}
// EXPORTS //
module.exports = gnrm2;
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