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dnrm2
Calculate the L2norm of a doubleprecision floatingpoint vector.
The L2norm is defined as
Installation
npm install @stdlib/blasbasednrm2
Usage
var dnrm2 = require( '@stdlib/blasbasednrm2' );
dnrm2( N, x, stride )
Computes the L2norm of a doubleprecision floatingpoint vector x
.
var Float64Array = require( '@stdlib/arrayfloat64' );
var x = new Float64Array( [ 1.0, 2.0, 2.0 ] );
var z = dnrm2( 3, x, 1 );
// returns 3.0
The function has the following parameters:
 N: number of indexed elements.

x: input
Float64Array
. 
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 Float64Array = require( '@stdlib/arrayfloat64' );
var x = new Float64Array( [ 1.0, 2.0, 2.0, 7.0, 2.0, 3.0, 4.0, 2.0 ] );
var z = dnrm2( 4, 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 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 z = dnrm2( 4, x1, 2 );
// returns 5.0
If either N
or stride
is less than or equal to 0
, the function returns 0
.
dnrm2.ndarray( N, x, stride, offset )
Computes the L2norm of a doubleprecision floatingpoint vector using alternative indexing semantics.
var Float64Array = require( '@stdlib/arrayfloat64' );
var x = new Float64Array( [ 1.0, 2.0, 2.0 ] );
var z = dnrm2.ndarray( 3, 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 Float64Array = require( '@stdlib/arrayfloat64' );
var x = new Float64Array( [ 2.0, 1.0, 2.0, 2.0, 2.0, 2.0, 3.0, 4.0 ] );
var z = dnrm2.ndarray( 4, x, 2, 1 );
// returns 5.0
Notes
Examples
var discreteUniform = require( '@stdlib/randomarraydiscreteuniform' );
var dnrm2 = require( '@stdlib/blasbasednrm2' );
var opts = {
'dtype': 'float64'
};
var x = discreteUniform( 10, 100, 100, opts );
console.log( x );
var out = dnrm2( x.length, x, 1 );
console.log( out );
See Also

@stdlib/blasbase/gnrm2
: calculate the L2norm of a 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 © 20162024. The Stdlib Authors.