time-to-botec/js/node_modules/@stdlib/math/strided/special/abs2/README.md

abs2

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

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( '' );
}