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@stdlib/math-strided-special-abs2

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Readme

abs2

$NPM version$ $Build Status$ $Coverage Status$ $dependencies$

Compute the squared absolute value for each element in a strided array.

Installation

npm install @stdlib/math-strided-special-abs2

Usage

var abs2 = require( '@stdlib/math-strided-special-abs2' );

abs2( N, x, strideX, y, strideY )

Computes the squared absolute value for each element in x and assigns the results to elements in y.

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 ] );

// Compute the squared absolute values in-place:
abs2( x.length, x, 1, x, 1 );
// x => <Float64Array>[ 4.0, 1.0, 9.0, 25.0, 16.0, 0.0, 1.0, 9.0 ]

The function accepts the following arguments:

N: number of indexed elements.
x: input array-like object.
strideX: index increment for x.
y: output array-like object.
strideY: index increment for y.

The N and stride parameters determine which elements in x and y are accessed at runtime. For example, to index every other value in x and the first N elements of y in reverse order,

var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

abs2( N, x, 2, y, -1 );
// y => <Float64Array>[ 25.0, 9.0, 1.0, 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' );
var floor = require( '@stdlib/math-base-special-floor' );

// Initial arrays...
var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var y0 = 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 y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

var N = floor( x0.length / 2 );

abs2( N, x1, -2, y1, 1 );
// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]

abs2.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )

Computes the squared absolute value for each element in x and assigns the result to an element in y using alternative indexing semantics.

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

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

abs2.ndarray( x.length, x, 1, 0, y, 1, 0 );
// y => <Float64Array>[ 1.0, 4.0, 9.0, 16.0, 25.0 ]

The function accepts the following additional arguments:

offsetX: starting index for x.
offsetY: starting index for y.

While typed array views mandate a view offset based on the underlying buffer, the offsetX and offsetY parameters support indexing semantics based on starting indices. For example, to index every other value in x starting from the second value and to index the last N elements in y,

var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

abs2.ndarray( N, x, 2, 1, y, -1, y.length-1 );
// y => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]

Notes

For output strided arrays having an integer data type, be careful of overflow, as overflow can lead to unexpected results.

Examples

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var filledarray = require( '@stdlib/array-filled' );
var dtypes = require( '@stdlib/array-dtypes' );
var gfillBy = require( '@stdlib/blas-ext-base-gfill-by' );
var abs2 = require( '@stdlib/math-strided-special-abs2' );

var dt;
var x;
var y;
var i;

dt = dtypes();
for ( i = 0; i < dt.length; i++ ) {
    x = filledarray( 0.0, 10, dt[ i ] );
    gfillBy( x.length, x, 1, discreteUniform( -10, 10 ) );
    console.log( x );

    y = filledarray( 0.0, x.length, dt[ i ] );
    console.log( y );

    abs2.ndarray( x.length, x, 1, 0, y, -1, y.length-1 );
    console.log( y );
    console.log( '' );
}

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

License

See LICENSE.

@stdlib/math-strided-special-abs2