@stdlib/blas-ext-base-dapx

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dapx

Add a constant to each element in a double-precision floating-point strided array.

Installation

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

Usage

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

dapx( N, alpha, x, stride )

Adds a constant alpha to each element in a double-precision floating-point strided array x.

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

dapx( x.length, 5.0, x, 1 );
// x => <Float64Array>[ 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 Float64Array.
• 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 Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var N = floor( x.length / 2 );

dapx( N, 5.0, x, 2 );
// x => <Float64Array>[ 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...
dapx( N, 5.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]

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

Adds a constant alpha to each element in a double-precision floating-point strided array x using alternative indexing semantics.

var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

dapx.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float64Array>[ 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 Float64Array = require( '@stdlib/array-float64' );

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

dapx.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float64Array>[ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]

Notes

• If N <= 0, both functions return x unchanged.

Examples

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

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 );

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

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See Also

• @stdlib/blas-ext/base/gapx: add a constant to each element in a strided array.
• @stdlib/blas-ext/base/sapx: add a constant to each element in a single-precision floating-point strided array.

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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

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