dznrm2

Compute the L2-norm of a complex double-precision floating-point vector.

Usage

var dznrm2 = require( '@stdlib/blas/base/dznrm2' );

dznrm2( N, zx, strideX )

Computes the L2-norm of a complex double-precision floating-point vector.

var Complex128Array = require( '@stdlib/array/complex128' );

var zx = new Complex128Array( [ 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 ] );

var norm = dznrm2( 4, zx, 1 );
// returns ~0.8

The function has the following parameters:

N: number of indexed elements.
zx: input Complex128Array.
strideX: index increment for zx.

The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to traverse every other value,

var Complex128Array = require( '@stdlib/array/complex128' );

var zx = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

var norm = dznrm2( 2, zx, 2 );
// returns ~4.6

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

var Complex128Array = require( '@stdlib/array/complex128' );

// Initial array:
var zx0 = new Complex128Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view:
var zx1 = new Complex128Array( zx0.buffer, zx0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Compute the L2-norm:
var norm = dznrm2( 2, zx1, 1 );
// returns ~9.3

dznrm2.ndarray( N, zx, strideX, offset )

Computes the L2-norm of a complex double-precision floating-point vector using alternative indexing semantics.

var Complex128Array = require( '@stdlib/array/complex128' );

var zx = new Complex128Array( [ 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 ] );

var norm = dznrm2.ndarray( 4, zx, 1, 0 );
// returns ~0.8

The function has the following additional parameters:

offsetX: starting index.

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 start from the second index,

var Complex128Array = require( '@stdlib/array/complex128' );

var zx = new Complex128Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

var norm = dznrm2.ndarray( 2, zx, 1, 1 );
// returns ~9.3

Notes

If N <= 0, both functions return 0.0.
dznrm2() corresponds to the BLAS level 1 function dznrm2.

Examples

var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var filledarrayBy = require( '@stdlib/array/filled-by' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var dznrm2 = require( '@stdlib/blas/base/dznrm2' );

function rand() {
    return new Complex128( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
}

var zx = filledarrayBy( 10, 'complex128', rand );
console.log( zx.toString() );

// Computes the L2-norm:
var norm = dznrm2( zx.length, zx, 1 );
console.log( norm );

C APIs

Usage

#include "stdlib/blas/base/dznrm2.h"

c_dznrm2( N, *ZX, strideX )

Computes the L2-norm of a complex double-precision floating-point vector.

const double zx[] = { 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 };

double norm = c_dznrm2( 4, (void *)zx, 1 );
// returns 0.8

The function accepts the following arguments:

N: [in] CBLAS_INT number of indexed elements.
ZX: [in] void* input array.
strideX: [in] CBLAS_INT index increment for ZX.

double c_dznrm2( const CBLAS_INT N, const void *ZX, const CBLAS_INT strideX );

c_dznrm2_ndarray( N, *ZX, strideX, offsetX )

Computes the L2-norm of a complex double-precision floating-point vector using alternative indexing semantics.

const double zx[] = { 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 };

double norm = c_dznrm2_ndarray( 4, (void *)zx, 1, 0 );
// returns 0.8

The function accepts the following arguments:

N: [in] CBLAS_INT number of indexed elements.
ZX: [in] void* input array.
strideX: [in] CBLAS_INT index increment for ZX.
offsetX: [in] CBLAS_INT starting index for ZX.

double c_dznrm2_ndarray( const CBLAS_INT N, const void *ZX, const CBLAS_INT strideX, const CBLAS_INT offsetX );

Examples

#include "stdlib/blas/base/dznrm2.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array of interleaved real and imaginary components:
    const double zx[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 };

    // Specify the number of elements:
    const int N = 4;

    // Specify stride length:
    const int strideX = 1;

    // Compute the L2-norm:
    double norm = c_dznrm2( N, (void *)zx, strideX );

    // Print the result:
    printf( "L2-norm: %lf\n", norm );

    // Compute the L2-norm using alternative indexing semantics:
    norm = c_dznrm2_ndarray( N, (void *)zx, -strideX, N-1 );

    // Print the result:
    printf( "L2-norm: %lf\n", norm );
}