srotm

Apply a modified Givens plane rotation.

Usage

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

srotm( N, x, strideX, y, strideY, param )

Applies a modified Givens 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 ] );
var param = new Float32Array( [ 0.0, 0.0, 2.0, -3.0, 0.0 ] );

srotm( 2, x, 2, y, 1, param );
// x => <Float32Array>[ ~-17.0, 2.0, ~-18.0, 4.0, 5.0 ]
// y => <Float32Array>[ ~8.0, ~13.0, 8.0, 9.0, 10.0 ]

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.
  • param: parameters for the modified Givens transformation

The N and stride parameters determine how values in the strided arrays are accessed at runtime. For example, to apply a modified Givens 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 ] );
var param = new Float32Array( [ 0.0, 0.0, 2.0, -3.0, 0.0 ] );

srotm( 3, x, 2, y, 2, param );
// x => <Float32Array>[ ~-20.0, 2.0, ~-24.0, 4.0, ~-28.0, 6.0 ]
// y => <Float32Array>[ ~9.0, 8.0, ~15.0, 10.0, ~21.0, 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 ] );
var y0 = new Float32Array( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );
var param = new Float32Array( [ 1.0, 0.0, 2.0, 3.0, 0.0 ] );

// 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

srotm( 2, x1, 1, y1, 1, param );
// x0 => <Float32Array>[ 1.0, ~9.0, ~10.0, 4.0, 5.0 ]
// y0 => <Float32Array>[ 6.0, 7.0, 8.0, ~-2.0, ~-3.0 ]

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

Applies a modified Givens 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 ] );
var param = new Float32Array( [ 0.0, 0.0, 2.0, -3.0, 0.0 ] );

srotm.ndarray( 2, x, 1, 0, y, 2, 1, param );
// x => <Float32Array>[ ~-20.0, ~-25.0, 3.0, 4.0, 5.0 ]
// y => <Float32Array>[ 6.0, ~9.0, 8.0, ~13.0, 10.0 ]

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 modified Givens plane rotation to every other element starting from the second 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 ] );
var param = new Float32Array( [ 0.0, 0.0, 2.0, -3.0, 0.0 ] );

srotm.ndarray( 3, x, 2, 1, y, 2, 1, param );
// x => <Float32Array>[ 1.0, ~-22.0, 3.0, ~-26.0, 5.0, ~-30.0 ]
// y => <Float32Array>[ 7.0, ~12.0, 9.0, ~18.0, 11.0, ~24.0 ]

Notes

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

Examples

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

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 );

var param = discreteUniform( 5, -5, 5, opts );
console.log( param );

// Apply a plane rotation:
srotm( x.length, x, 1, y, 1, param );
console.log( x );
console.log( y );

C APIs

Usage

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

c_srotm( N, *X, strideX, *Y, strideY, param )

Applies a modified Givens 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 };
const float param[5] = { 0.0f, 0.0f, 2.0f, -3.0f, 0.0f };

c_srotm( 5, x, 1, y, 1, param );

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.
  • param: [in] float parameters for the modified Givens transformation.
void c_srotm( const CBLAS_INT N, float *X, const CBLAS_INT strideX, float *Y, const CBLAS_INT strideY, const float *param );

c_srotm_ndarray( N, *X, strideX, offsetX, *Y, strideY, offsetY, param )

Applies a modified Givens plane rotation using alternative indexing semantics.

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };
float y[] = { 6.0f, 7.0f, 8.0f, 9.0f, 10.0f };
const float param[5] = { 0.0f, 0.0f, 2.0f, -3.0f, 0.0f };

c_srotm_ndarray( 5, x, 1, 0, y, 1, 0, param );

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.
  • offsetX: [in] CBLAS_INT starting index for X.
  • Y: [inout] float* second input array.
  • strideY: [in] CBLAS_INT index increment for Y.
  • offsetY: [in] CBLAS_INT starting index for Y.
  • param: [in] float parameters for the modified Givens transformation.
void c_srotm_ndarray( const CBLAS_INT N, float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, float *Y, const CBLAS_INT strideY, const CBLAS_INT offsetY, const float *param );

Examples

#include "stdlib/blas/base/srotm.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 parameters for the modified Givens transformation:
    const float param[5] = { 0.0f, 0.0f, 2.0f, -3.0f, 0.0f };

    // Apply plane rotation:
    c_srotm( N, x, strideX, y, strideY, param );

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

    // Apply plane rotation:
    c_srotm_ndarray( N, x, -strideX, N-1, y, -strideY, N-1, param );

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