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gwxsa

Subtract a scalar constant from each element in a strided array x and assign the results to elements in a strided array w.

This BLAS extension implements the operation

$$\mathbf{w} = \mathbf{x} - \alpha$$

This API is complementary to the package @stdlib/blas-ext/base/gwapx.

Installation

npm install @stdlib/blas-ext-base-gwxsa

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

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

gwxsa( N, alpha, x, strideX, w, strideW )

Subtracts a scalar constant from each element in a strided array x and assigns the results to elements in a strided array w.

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var w = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

gwxsa( x.length, 5.0, x, 1, w, 1 );
// w => [ -4.0, -3.0, -2.0, -1.0, 0.0 ]

The function has the following parameters:

• N: number of indexed elements.
• alpha: scalar constant.
• x: input Array or typed array.
• strideX: stride length for x.
• w: output Array or typed array.
• strideW: stride length for w.

The N and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to subtract alpha from every other element in x and assign the results to every other element in w:

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var w = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

gwxsa( 3, 5.0, x, 2, w, 2 );
// w => [ -4.0, 0.0, -2.0, 0.0, 0.0, 0.0 ]

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 w0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var w1 = new Float64Array( w0.buffer, w0.BYTES_PER_ELEMENT*2 ); // start at 3rd element

gwxsa( 3, 5.0, x1, 1, w1, 1 );
// w0 => <Float64Array>[ 0.0, 0.0, -3.0, -2.0, -1.0, 0.0 ]

gwxsa.ndarray( N, alpha, x, strideX, offsetX, w, strideW, offsetW )

Subtracts a scalar constant from each element in a strided array x and assigns the results to elements in a strided array w using alternative indexing semantics.

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var w = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

gwxsa.ndarray( x.length, 5.0, x, 1, 0, w, 1, 0 );
// w => [ -4.0, -3.0, -2.0, -1.0, 0.0 ]

The function has the following additional parameters:

• offsetX: starting index for x.
• offsetW: starting index for w.

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 subtract alpha from the last three elements of x and assign the results to the last three elements of w:

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var w = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

gwxsa.ndarray( 3, 5.0, x, 1, x.length-3, w, 1, w.length-3 );
// w => [ 0.0, 0.0, -2.0, -1.0, 0.0 ]

Notes

• If N <= 0, both functions return w unchanged.
• Both functions support array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-base/accessor).

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var logEach = require( '@stdlib/console-log-each' );
var gwxsa = require( '@stdlib/blas-ext-base-gwxsa' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 10, -100, 100, opts );
var w = discreteUniform( 10, -100, 100, opts );

gwxsa( x.length, 5.0, x, 1, w, 1 );
logEach( '%d - %d = %d', x, 5.0, w );

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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.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.