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

drsqrt

Compute the reciprocal square root for each element in a double-precision floating-point strided array.

Usage

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

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

Computes the reciprocal square root for each element in a double-precision floating-point strided array x and assigns the results to elements in a double-precision floating-point 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:
drsqrt( 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 Float64Array.
• strideX: index increment for x.
• y: output Float64Array.
• 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 to index 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 ] );

drsqrt( 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

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

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

Computes the reciprocal square root for each element in a double-precision floating-point strided array x and assigns the results to elements in a double-precision floating-point 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 ] );

drsqrt.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 ] );

drsqrt.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' );
var Float64Array = require( '@stdlib/array/float64' );
var drsqrt = require( '@stdlib/math/strided/special/drsqrt' );

var x = new Float64Array( 10 );
var y = new Float64Array( 10 );

var i;
for ( i = 0; i < x.length; i++ ) {
    x[ i ] = uniform( 0.0, 200.0 );
}
console.log( x );
console.log( y );

drsqrt.ndarray( x.length, x, 1, 0, y, -1, y.length-1 );
console.log( y );

---

C APIs

Usage

#include "stdlib/math/strided/special/drsqrt.h"

stdlib_strided_drsqrt( N, *X, strideX, *Y, strideY )

Computes the reciprocal square root for each element in a double-precision floating-point strided array X and assigns the results to elements in a double-precision floating-point strided array Y.

#include <stdint.h>

double X[] = { 0.0, 4.0, 9.0, 12.0, 24.0, 64.0, 81.0, 101.0 };
double Y[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

int64_t N = 4;

stdlib_strided_drsqrt( N, X, 2, Y, 2 );

The function accepts the following arguments:

• N: [in] int64_t number of indexed elements.
• X: [in] double* input array.
• strideX: [in] int64_t index increment for X.
• Y: [out] double* output array.
• strideY: [in] int64_t index increment for Y.

void stdlib_strided_drsqrt( const int64_t N, const double *X, const int64_t strideX, double *Y, const int64_t strideY );

Examples

#include "stdlib/math/strided/special/drsqrt.h"
#include <stdint.h>
#include <stdio.h>

int main() {
    // Create an input strided array:
    double X[] = { 0.0, 4.0, 9.0, 12.0, 24.0, 64.0, 81.0, 101.0 };

    // Create an output strided array:
    double Y[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

    // Specify the number of elements:
    int64_t N = 4;

    // Specify the stride lengths:
    int64_t strideX = 2;
    int64_t strideY = 2;

    // Compute the results:
    stdlib_strided_drsqrt( N, X, strideX, Y, strideY );

    // Print the results:
    for ( int i = 0; i < 8; i++ ) {
        printf( "Y[ %i ] = %lf\n", i, Y[ i ] );
    }
}