README.md

zswap

Interchange two complex double-precision floating-point vectors.

This BLAS level 1 routine interchanges complex double-precision floating-point vectors x and y. The operation is performed in-place, with x being overwritten with the values from y, and y being overwritten with the values from x.

Usage

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

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

Interchange two complex double-precision floating-point vectors.

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

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zswap( x.length, x, 1, y, 1 );

var z = y.get( 0 );
// returns <Complex128>

var re = real( z );
// returns 1.0

var im = imag( z );
// returns 2.0

z = x.get( 0 );
// returns <Complex128>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0

The function has the following parameters:

• N: number of indexed elements.
• x: first input Complex128Array.
• strideX: index increment for x.
• y: second input Complex128Array.
• strideY: index increment for y.

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

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

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zswap( 2, x, -2, y, 1 );

var z = y.get( 0 );
// returns <Complex128>

var re = real( z );
// returns 5.0

var im = imag( z );
// returns 6.0

z = x.get( 0 );
// returns <Complex128>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0

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

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

// Initial arrays...
var x0 = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y0 = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Complex128Array( y0.buffer, y0.BYTES_PER_ELEMENT*2 ); // start at 3rd element

// Interchange in reverse order every other value from `x1` into `y1`...
zswap( 2, x1, -2, y1, 1 );

var z = y0.get( 2 );
// returns <Complex128>

var re = real( z );
// returns 7.0

var im = imag( z );
// returns 8.0

z = x0.get( 1 );
// returns <Complex128>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0

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

Interchange two complex double-precision floating-point vectors using alternative indexing semantics.

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

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zswap.ndarray( x.length, x, 1, 0, y, 1, 0 );

var z = y.get( 0 );
// returns <Complex128>

var re = real( z );
// returns 1.0

var im = imag( z );
// returns 2.0

z = x.get( 0 );
// returns <Complex128>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0

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 interchange every other value in x starting from the second value into the last N elements in y where x[i] = y[n], x[i+2] = y[n-1], and so on,

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

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zswap.ndarray( 2, x, 2, 1, y, -1, y.length-1 );

var z = y.get( y.length-1 );
// returns <Complex128>

var re = real( z );
// returns 3.0

var im = imag( z );
// returns 4.0

z = x.get( x.length-1 );
// returns <Complex128>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0

Notes

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

Examples

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

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

var x = filledarrayBy( 10, 'complex128', rand );
console.log( x.get( 0 ).toString() );

var y = filledarrayBy( 10, 'complex128', rand );
console.log( y.get( 0 ).toString() );

// Swap elements in `x` into `y` starting from the end of `y`:
zswap( x.length, x, 1, y, -1 );
console.log( x.get( x.length-1 ).toString() );
console.log( y.get( y.length-1 ).toString() );