@stdlib/blas-base-srot v0.1.0

srot

Apply a plane rotation.

This BLAS level 1 routine applies a real plane rotation to real single-precision floating-point vectors. The plane rotation is applied to N points, where the points to be rotated are contained in vectors x and y and where the cosine and sine of the angle of rotation are c and s, respectively. The operation is as follows:

where x_i and y_i are the individual elements on which the rotation is applied.

Installation

npm install @stdlib/blas-base-srot

Usage

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

srot( N, x, strideX, y, strideY, c, s )

Applies a plane rotation.

var Float32Array = require( '@stdlib/array-float32' );

var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
var y = new Float32Array( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );

srot( x.length, x, 1, y, 1, 0.8, 0.6 );
// x => <Float32Array>[ ~4.4, ~5.8, ~7.2, ~8.6, 10.0 ]
// y => <Float32Array>[ ~4.2, ~4.4, ~4.6, ~4.8, 5.0 ]

The function has the following parameters:

• N: number of indexed elements.
• x: first input Float32Array.
• strideX: index increment for x.
• y: second input Float32Array.
• strideY: index increment for y.
• c: cosine of the angle of rotation.
• s: sine of the angle of rotation.

The N and stride parameters determine how values in the strided arrays are accessed at runtime. For example, to apply a plane rotation to every other element,

var Float32Array = require( '@stdlib/array-float32' );

var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float32Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

srot( 3, x, 2, y, 2, 0.8, 0.6 );
// x => <Float32Array>[ ~5.0, 2.0, ~7.8, 4.0, ~10.6, 6.0 ]
// y => <Float32Array>[ 5.0, 8.0, ~5.4, 10.0, ~5.8, 12.0 ]

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

var Float32Array = require( '@stdlib/array-float32' );

// Initial arrays...
var x0 = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y0 = new Float32Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Create offset views...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float32Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

srot( 3, x1, 1, y1, 1, 0.8, 0.6 );
// x0 => <Float32Array>[ 1.0, ~7.6, 9.0, ~10.4, 5.0, 6.0 ]
// y0 => <Float32Array>[ 7.0, 8.0, 9.0, ~6.8, 7.0, ~7.2 ]

srot.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, c, s )

Applies a plane rotation using alternative indexing semantics.

var Float32Array = require( '@stdlib/array-float32' );

var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
var y = new Float32Array( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );

srot.ndarray( 4, x, 1, 1, y, 1, 1, 0.8, 0.6 );
// x => <Float32Array>[ 1.0, ~5.8, ~7.2, ~8.6, 10.0 ]
// y => <Float32Array>[ 6.0, ~4.4, ~4.6, ~4.8, 5.0 ]

The function has the following additional parameters:

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

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to apply a plane rotation to every other element starting from third element,...,

var Float32Array = require( '@stdlib/array-float32' );

var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float32Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

srot.ndarray( 2, x, 2, 2, y, 2, 2, 0.8, 0.6 );
// x => <Float32Array>[ 1.0, 2.0, ~7.8, 4.0, ~10.6, 6.0 ]
// y => <Float32Array>[ 7.0, 8.0, ~5.4, 10.0, ~5.8, 12.0 ]

Notes

• If N <= 0, both functions leave x and y unchanged.
• srot() corresponds to the BLAS level 1 function srot.

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var srot = require( '@stdlib/blas-base-srot' );

var opts = {
    'dtype': 'float32'
};
var x = discreteUniform( 10, 0, 500, opts );
console.log( x );

var y = discreteUniform( x.length, 0, 255, opts );
console.log( y );

// Applies a plane rotation :
srot( x.length, x, 1, y, 1, 0.8, 0.6 );
console.log( x );
console.log( y );

C APIs

Usage

#include "stdlib/blas/base/srot.h"

c_srot( N, *X, strideX, *Y, strideY, c, s )

Applies a plane rotation.

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };
float y[] = { 6.0f, 7.0f, 8.0f, 9.0f, 10.0f };

c_drot( 5, x, 1, y, 1, 0.8f, 0.6f );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• X: [inout] float* first input array.
• strideX: [in] CBLAS_INT index increment for X.
• Y: [inout] float* second input array.
• strideY: [in] CBLAS_INT index increment for Y.
• c: [in] float cosine of the angle of rotation.
• s: [in] float sine of the angle of rotation.

void c_drot( const CBLAS_INT N, float *X, const CBLAS_INT strideX, float *Y, const CBLAS_INT strideY, const float c, const float s );

Examples

#include "stdlib/blas/base/drot.h"
#include <stdio.h>

int main( void ) {
    // Create strided arrays:
    float x[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };
    float y[] = { 6.0f, 7.0f, 8.0f, 9.0f, 10.0f };

    // Specify the number of elements:
    const int N = 5;

    // Specify stride lengths:
    const int strideX = 1;
    const int strideY = 1;

    // Specify angle of rotation:
    const float c = 0.8f;
    const float s = 0.6f;

    // Apply plane rotation:
    c_drot( N, x, strideX, y, strideY, c, s );

    // Print the result:
    for ( int i = 0; i < 5; i++ ) {
        printf( "x[ %i ] = %f, y[ %i ] = %f\n", i, x[ i ], i, y[ i ] );
    }
}

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.

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License

See LICENSE.

Copyright

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