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gnrm2
Calculate the L2norm of a vector.
The L2norm is defined as
Installation
npm install @stdlib/blasbasegnrm2
Usage
var gnrm2 = require( '@stdlib/blasbasegnrm2' );
gnrm2( N, x, stride )
Computes the L2norm of a vector x
.
var x = [ 1.0, 2.0, 2.0 ];
var z = gnrm2( x.length, x, 1 );
// returns 3.0
The function has the following parameters:
 N: number of indexed elements.

x: input
Array
ortyped array
. 
stride: index increment for
x
.
The N
and stride
parameters determine which elements in x
are accessed at runtime. For example, to compute the L2norm of every other element in x
,
var floor = require( '@stdlib/mathbasespecialfloor' );
var x = [ 1.0, 2.0, 2.0, 7.0, 2.0, 3.0, 4.0, 2.0 ];
var N = floor( x.length / 2 );
var z = gnrm2( N, x, 2 );
// returns 5.0
Note that indexing is relative to the first index. To introduce an offset, use typed array
views.
var Float64Array = require( '@stdlib/arrayfloat64' );
var floor = require( '@stdlib/mathbasespecialfloor' );
var x0 = new Float64Array( [ 2.0, 1.0, 2.0, 2.0, 2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length / 2 );
var z = gnrm2( N, x1, 2 );
// returns 5.0
If either N
or stride
is less than or equal to 0
, the function returns 0
.
gnrm2.ndarray( N, x, stride, offset )
Computes the L2norm of a vector using alternative indexing semantics.
var x = [ 1.0, 2.0, 2.0 ];
var z = gnrm2.ndarray( x.length, x, 1, 0 );
// returns 3.0
The function has the following additional parameters:

offset: starting index for
x
.
While typed array
views mandate a view offset based on the underlying buffer
, the offset
parameter supports indexing semantics based on a starting index. For example, to calculate the L2norm for every other value in x
starting from the second value
var floor = require( '@stdlib/mathbasespecialfloor' );
var x = [ 2.0, 1.0, 2.0, 2.0, 2.0, 2.0, 3.0, 4.0 ];
var N = floor( x.length / 2 );
var z = gnrm2.ndarray( N, x, 2, 1 );
// returns 5.0
Notes
 If
N <= 0
, both functions return0.0
. 
gnrm2()
corresponds to the BLAS level 1 functiondnrm2
with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (dnrm2
,snrm2
, etc.) are likely to be significantly more performant.
Examples
var randu = require( '@stdlib/randombaserandu' );
var round = require( '@stdlib/mathbasespecialround' );
var Float64Array = require( '@stdlib/arrayfloat64' );
var gnrm2 = require( '@stdlib/blasbasegnrm2' );
var x;
var i;
x = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
x[ i ] = round( randu()*100.0 );
}
console.log( x );
var z = gnrm2( x.length, x, 1 );
console.log( z );
See Also

@stdlib/blasbase/dnrm2
: calculate the L2norm of a doubleprecision floatingpoint vector. 
@stdlib/blasbase/snrm2
: calculate the L2norm of a singleprecision floatingpoint vector.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 20162023. The Stdlib Authors.