@stdlib/blas-base-dswap NPM

dswap

Interchange two double-precision floating-point vectors.

Installation

npm install @stdlib/blas-base-dswap

Usage

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

dswap( N, x, strideX, y, strideY )

Interchanges vectors x and y.

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
var y = new Float64Array( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );

dswap( x.length, x, 1, y, 1 );
// x => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
// y => <Float64Array>[ 1.0, 2.0, 3.0, 4.0, 5.0 ]

The function has the following parameters:

N: number of indexed elements.
x: first input Float64Array.
strideX: index increment for x.
y: second input Float64Array.
strideY: index increment for y.

The N and stride parameters determine how values in the strided arrays are accessed at runtime. For example, to swap in reverse order every other value in x with the first N elements of y,

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

dswap( 3, x, -2, y, 1 );
// x => <Float64Array>[ 9.0, 2.0, 8.0, 4.0, 7.0, 6.0 ]
// y => <Float64Array>[ 5.0, 3.0, 1.0, 10.0, 11.0, 12.0 ]

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

var Float64Array = require( '@stdlib/array-float64' );

// Initial arrays...
var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y0 = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

// Swap in reverse order every other value from `x1` with `y1`...
dswap( 3, x1, -2, y1, 1 );
// x0 => <Float64Array>[ 1.0, 12.0, 3.0, 11.0, 5.0, 10.0 ]
// y0 => <Float64Array>[ 7.0, 8.0, 9.0, 6.0, 4.0, 2.0 ]

dswap.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )

Interchanges vectors x and y using alternative indexing semantics.

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
var y = new Float64Array( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );

dswap.ndarray( x.length, x, 1, 0, y, 1, 0 );
// x => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
// y => <Float64Array>[ 1.0, 2.0, 3.0, 4.0, 5.0 ]

The function has the following additional parameters:

offsetX: starting index for x.
offsetY: starting index for y.

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to swap every other value in x starting from the second value with the last N elements in y where x[i] = y[n], x[i+2] = y[n-1],...,

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

dswap.ndarray( 3, x, 2, 1, y, -1, y.length-1 );
// x => <Float64Array>[ 1.0, 12.0, 3.0, 11.0, 5.0, 10.0 ]
// y => <Float64Array>[ 7.0, 8.0, 9.0, 6.0, 4.0, 2.0 ]

Notes

If N <= 0, both functions leave x and y unchanged.
dswap() corresponds to the BLAS level 1 function dswap.

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var dswap = require( '@stdlib/blas-base-dswap' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 10, 0, 500, opts );
console.log( x );

var y = discreteUniform( x.length, 0, 255, opts );
console.log( y );

// Swap elements in `x` and `y` starting from the end of `y`:
dswap( x.length, x, 1, y, -1 );
console.log( x );
console.log( y );

C APIs

Usage

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

c_dswap( N, X, strideX, Y, strideY )

Interchanges two double-precision floating-point vectors.

double x[] = { 1.0, 2.0, 3.0, 4.0 };
double y[] = { 0.0, 0.0, 0.0, 0.0 };

c_dswap( 4, x, 1, y, 1 );

The function accepts the following arguments:

N: [in] CBLAS_INT number of indexed elements.
X: [inout] double* first input array.
strideX: [in] CBLAS_INT index increment for X.
Y: [inout] double* first input array.
strideY: [in] CBLAS_INT index increment for Y.

void c_dswap( const CBLAS_INT N, double *X, const CBLAS_INT strideX, double *Y, const CBLAS_INT strideY );

Examples

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

int main( void ) {
    // Create strided arrays:
    double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 };
    double y[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

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

    // Specify stride lengths:
    const int strideX = 2;
    const int strideY = -2;

    // Interchange elements:
    c_dswap( N, x, strideX, y, strideY );

    // Print the result:
    for ( int i = 0; i < 8; i++ ) {
        printf( "x[ %i ] = %lf\n", i, x[ i ] );
        printf( "y[ %i ] = %lf\n", i, y[ i ] );
    }
}

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.