@stdlib/blas-base-dswap
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0.2.1 • Public • Published
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dswap

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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 );

See Also


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.

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.

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npm i @stdlib/blas-base-dswap

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