@stdlib/blas-ext-base-gapx

Add a constant to each element in a strided array.

Usage no npm install needed!

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README

gapx

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Add a constant to each element in a strided array.

Installation

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

Usage

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

gapx( N, alpha, x, stride )

Adds a constant alpha to each element in a strided array x.

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

gapx( x.length, 5.0, x, 1 );
// x => [ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • alpha: scalar constant.
  • x: input Array or typed array.
  • stride: index increment.

The N and stride parameters determine which elements in x are accessed at runtime. For example, to add a constant to every other element

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

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
var N = floor( x.length / 2 );

gapx( N, 5.0, x, 2 );
// x => [ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -3.0 ]

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 array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length/2 );

// Add a constant to every other element...
gapx( N, 5.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]

gapx.ndarray( N, alpha, x, stride, offset )

Adds a constant alpha to each element in a strided array x using alternative indexing semantics.

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

gapx.ndarray( x.length, 5.0, x, 1, 0 );
// x => [ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]

The function has the following additional parameters:

  • offset: starting index.

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 access only the last three elements of x

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

gapx.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]

Notes

  • If N <= 0, both functions return x unchanged.
  • Depending on the environment, the typed versions (dapx, sapx, etc.) are likely to be significantly more performant.

Examples

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

var rand;
var sign;
var x;
var i;

x = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
    rand = round( randu()*100.0 );
    sign = randu();
    if ( sign < 0.5 ) {
        sign = -1.0;
    } else {
        sign = 1.0;
    }
    x[ i ] = sign * rand;
}
console.log( x );

gapx( x.length, 5.0, x, 1 );
console.log( x );

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 © 2016-2022. The Stdlib Authors.