@stdlib/blas-base-srot

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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 );

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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 ] );
    }
}

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Notice

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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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