gswap

Interchange two vectors.

Usage

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

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

Interchanges vectors x and y.

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

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

The function has the following parameters:

• N: number of values to swap.
• x: first input Array or typed array.
• strideX: index increment for x.
• y: second input Array or typed array.
• strideY: index increment for y.

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

var floor = require( '@stdlib/math/base/special/floor' );

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

var N = floor( x.length / 2 );

gswap( N, x, -2, y, 1 );
// x => [ 1.0, 7.0, 3.0, 8.0, 5.0, 9.0 ]
// y => [ 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' );
var floor = require( '@stdlib/math/base/special/floor' );

// 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

var N = floor( x0.length / 2 );

// Swap in reverse order every other value from `x1` with `y1`...
gswap( N, 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 ]

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

Interchanges vectors x and y using alternative indexing semantics.

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

gswap.ndarray( x.length, x, 1, 0, y, 1, 0 );
// x => [ 6.0, 7.0, 8.0, 9.0, 10.0 ]
// y => [ 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 offsetX and offsetY 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 floor = require( '@stdlib/math/base/special/floor' );

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 ] );

var N = floor( x.length / 2 );

gswap.ndarray( N, x, 2, 1, y, -1, y.length-1 );
// x => <Float64Array>[ 1.0, 12.0, 11.0, 10.0, 5.0, 6.0 ]
// 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.
• gswap() corresponds to the BLAS level 1 function dswap with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (dswap, sswap, etc.) are likely to be significantly more performant.

Examples

var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var Float64Array = require( '@stdlib/array/float64' );
var gswap = require( '@stdlib/blas/base/gswap' );

var x;
var y;
var i;

x = new Float64Array( 10 );
y = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
    x[ i ] = round( randu()*500.0 );
    y[ i ] = round( randu()*255.0 );
}
console.log( x );
console.log( y );

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