dnrm2

Computes the L2 norm of x.

The L2 norm is defined as

Installation

$ npm install blas-dnrm2

Usage

var dnrm2 = require( 'blas-dnrm2' );

dnrm2( N, x, stride, offset )

Computes the L2 norm.

var x = [ -2, 1, 3, -5, 4, 0, -1, -3 ];

var nrm = dnrm2( x.length, x, 1, 0 );
// returns ~8.062

The function accepts the following parameters:

• N: number of accessed elements.
• x: input array or typed array.
• stride: index increment.
• offset: starting index.

The N, stride, and offset parameters determine which elements in x are accessed when computing the L2 norm. For example, to select every other value starting from the second element,

var x = [ -2, 1, 3, -5, 4, 0, -1, -3 ];

var N = Math.floor( x.length / 2 );
var stride = 2;
var offset = 1;

var nrm = dnrm2( N, x, stride, offset );
// returns ~5.916

If any of the following conditions are met

• N < 0
• stride <= 0
• offset < 0

the function returns undefined. If N = 0, the function returns 0.

Notes

• This module corresponds to the BLAS level 1 function dnrm2.

Examples

var dnrm2 = require( 'blas-dnrm2' );

var rand;
var sign;
var x;
var i;

x = new Float64Array( 100 );
for ( i = 0; i < x.length; i++ ) {
	rand = Math.round( Math.random() * 100 );
	sign = Math.random();
	if ( sign < 0.5 ) {
		sign = -1;
	} else {
		sign = 1;
	}
	x[ i ] = sign * rand;
}

console.log( dnrm2( x.length, x, 1, 0 ) );

To run the example code from the top-level application directory,

$ node ./examples/index.js

References

• Dahlquist, Germund and Bjorck, Ake. Numerical Methods in Scientific Computing.
• Blue, James (1978) "A Portable Fortran Program To Find the Euclidean Norm of a Vector". ACM Transactions on Mathematical Software.
• Higham, Nicholas J. Accuracy and Stability of Numerical Algorithms, Second Edition.

This module implements a one-pass algorithm proposed by S.J. Hammarling.

Tests

Unit

This repository uses tape for unit tests. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

License

MIT license.

Copyright

Copyright © 2016. The Compute.io Authors.