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zscal

Scale a double-precision complex floating-point vector by a double-precision complex floating-point constant.

Usage

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

zscal.main( N, alpha, x, strideX )

Scales values from x by alpha.

var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.main( x.length, alpha, x, 1 );
// x => <Complex128Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • alpha: scalar Complex128 constant.
  • x: input Complex128Array.
  • strideX: index increment for x.

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

var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.main( 2, alpha, x, 2 );
// x => <Complex128Array>[ -2.0, 6.0, 3.0, 4.0, -2.0, 22.0 ]

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

var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Initial array:
var x0 = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Create an offset view:
var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Scales every other value from `x1` by `alpha`...
zscal.main( 3, alpha, x1, 1 );
// x0 => <Complex128Array>[ 1.0, 2.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0 ]

zscal.ndarray( N, alpha, x, strideX, offsetX )

Scales values from x by alpha using alternative indexing semantics.

var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.ndarray( x.length, alpha, x, 1, 0 );
// x => <Complex128Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0 ]

The function has the following additional parameters:

  • offsetX: starting index for x.

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 scale every other value in the input strided array starting from the second element,

var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var alpha = new Complex128( 2.0, 2.0 );

zscal.ndarray( 2, alpha, x, 2, 1 );
// x => <Complex128Array>[ 1.0, 2.0, -2.0, 14.0, 5.0, 6.0, -2.0, 30.0 ]

Module

zscal.Module( memory )

Returns a new WebAssembly module wrapper instance which uses the provided WebAssembly memory instance as its underlying memory.

var Memory = require( '@stdlib/wasm/memory' );

// Create a new memory instance with an initial size of 10 pages (640KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();

zscal.Module.prototype.main( N, zap, zxp, sx )

Scales values from x by alpha .

var Memory = require( '@stdlib/wasm/memory' );
var oneTo = require( '@stdlib/array/one-to' );
var ones = require( '@stdlib/array/ones' );
var zeros = require( '@stdlib/array/zeros' );
var bytesPerElement = require( '@stdlib/ndarray/base/bytes-per-element' );
var Float64Array = require( '@stdlib/array/float64' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex64 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Create a new memory instance with an initial size of 10 pages (320KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();

// Define a vector data type:
var dtype = 'complex128';

// Specify a vector length:
var N = 5;

// Define a pointer (i.e., byte offset) for storing the input vector:
var xptr = 0;

// Define a pointer for storing a complex number:
var zptr = N * bytesPerElement( dtype );

// Write vector values to module memory:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );
mod.write( xptr, x );

// Write a complex number to module memory:
mod.write( zptr, new Float64Array( [ 2.0, 2.0 ] ) );

// Perform computation:
mod.main( N, zptr, xptr, 1 );

// Read out the results:
var view = zeros( N, dtype );
mod.read( xptr, view );

console.log( reinterpretComplex64( view, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • zap: pointer (i.e., byte offset) to a scalar Complex128 constant.
  • zxp: input Complex128Array pointer (i.e., byte offset).
  • sx: index increment for x.

zscal.Module.prototype.ndarray( N, zap, zxp, sx, ox )

Scales values from x by alpha using alternative indexing semantics.

var Memory = require( '@stdlib/wasm/memory' );
var oneTo = require( '@stdlib/array/one-to' );
var ones = require( '@stdlib/array/ones' );
var zeros = require( '@stdlib/array/zeros' );
var bytesPerElement = require( '@stdlib/ndarray/base/bytes-per-element' );
var Float64Array = require( '@stdlib/array/float64' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex64 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Create a new memory instance with an initial size of 10 pages (320KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();

// Define a vector data type:
var dtype = 'complex128';

// Specify a vector length:
var N = 5;

// Define a pointer (i.e., byte offset) for storing the input vector:
var xptr = 0;

// Define a pointer for storing a complex number:
var zptr = N * bytesPerElement( dtype );

// Write vector values to module memory:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );
mod.write( xptr, x );

// Write a complex number to module memory:
mod.write( zptr, new Float64Array( [ 2.0, 2.0 ] ) );

// Perform computation:
mod.ndarray( N, zptr, xptr, 1, 0 );

// Read out the results:
var view = zeros( N, dtype );
mod.read( xptr, view );

console.log( reinterpretComplex64( view, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]

The function has the following additional parameters:

  • ox: starting index for x.

Notes

  • If N <= 0, x is left unchanged.
  • This package implements routines using WebAssembly. When provided arrays which are not allocated on a zscal module memory instance, data must be explicitly copied to module memory prior to computation. Data movement may entail a performance cost, and, thus, if you are using arrays external to module memory, you should prefer using @stdlib/blas/base/zscal. However, if working with arrays which are allocated and explicitly managed on module memory, you can achieve better performance when compared to the pure JavaScript implementations found in @stdlib/blas/base/zscal. Beware that such performance gains may come at the cost of additional complexity when having to perform manual memory management. Choosing between implementations depends heavily on the particular needs and constraints of your application, with no one choice universally better than the other.
  • zscal() corresponds to the BLAS level 1 function zscal.

Examples

var hasWebAssemblySupport = require( '@stdlib/assert/has-wasm-support' );
var oneTo = require( '@stdlib/array/one-to' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex64 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Specify a vector length:
var N = 5;

// Create an input array:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );

// Create a complex number:
var alpha = new Complex128( 2.0, 2.0 );

// Perform computation:
zscal.ndarray( N, alpha, x, 1, 0 );

// Print the results:
console.log( reinterpretComplex64( x, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]