time-to-botec/squiggle/node_modules/@stdlib/math/strided/special/rsqrt/README.md

rsqrt

Compute the reciprocal square root for each element in a strided array.

The reciprocal of the principal square root is defined as

Usage

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

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

Computes the reciprocal square root for each element in a strided array x and assigns the results to elements in a strided array y.

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

var x = new Float64Array( [ 0.0, 4.0, 9.0, 12.0, 24.0 ] );

// Perform operation in-place:
rsqrt( x.length, x, 1, x, 1 );
// x => <Float64Array>[ Infinity, 0.5, ~0.333, ~0.289, ~0.204 ]

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 x = new Float64Array( [ 0.0, 4.0, 9.0, 12.0, 24.0, 64.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

rsqrt( 3, x, 2, y, -1 );
// y => <Float64Array>[ ~0.204, ~0.333, Infinity, 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( [ 0.0, 4.0, 9.0, 12.0, 24.0, 64.0 ] );
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

rsqrt( 3, x1, -2, y1, 1 );
// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 0.125, ~0.289, 0.5 ]

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

Computes the reciprocal square root for each element in a strided array x and assigns the results to elements in a strided array y using alternative indexing semantics.

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

var x = new Float64Array( [ 0.0, 4.0, 9.0, 12.0, 24.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );

rsqrt.ndarray( x.length, x, 1, 0, y, 1, 0 );
// y => <Float64Array>[ Infinity, 0.5, ~0.333, ~0.289, ~0.204 ]

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 x = new Float64Array( [ 0.0, 4.0, 9.0, 12.0, 24.0, 64.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

rsqrt.ndarray( 3, x, 2, 1, y, -1, y.length-1 );
// y => <Float64Array>[ 0.0, 0.0, 0.0, 0.125, ~0.289, 0.5 ]

Examples

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

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, uniform( 0.0, 100.0 ) );
    console.log( x );

    y = filledarray( 0.0, x.length, 'generic' );
    console.log( y );

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