gaxpy
Multiply
x
by a constantalpha
and add the result toy
.
Usage
var gaxpy = require( '@stdlib/blas/base/gaxpy' );
gaxpy( N, alpha, x, strideX, y, strideY )
Multiplies x
by a constant alpha
and adds the result to y
.
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var y = [ 1.0, 1.0, 1.0, 1.0, 1.0 ];
var alpha = 5.0;
gaxpy( x.length, alpha, x, 1, y, 1 );
// y => [ 6.0, 11.0, 16.0, 21.0, 26.0 ]
The function has the following parameters:
- N: number of indexed elements.
- alpha:
numeric
constant. - x: input
Array
ortyped array
. - strideX: index increment for
x
. - y: input
Array
ortyped array
. - strideY: index increment for
y
.
The N
and stride
parameters determine which elements in x
and y
are accessed at runtime. For example, to multiply every other value in x
by alpha
and add the result to the first N
elements of y
in reverse order,
var floor = require( '@stdlib/math/base/special/floor' );
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0 ];
var alpha = 5.0;
var N = floor( x.length / 2 );
gaxpy( N, alpha, x, 2, y, -1 );
// y => [ 26.0, 16.0, 6.0, 1.0, 1.0, 1.0 ]
Note that indexing is relative to the first index. To introduce an offset, use typed array
views.
var Float64Array = require( '@stdlib/array/float64' );
var floor = require( '@stdlib/math/base/special/floor' );
// Initial arrays...
var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y0 = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
// 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
var N = floor( x0.length / 2 );
gaxpy( N, 5.0, x1, -2, y1, 1 );
// y0 => <Float64Array>[ 7.0, 8.0, 9.0, 40.0, 31.0, 22.0 ]
gaxpy.ndarray( N, alpha, x, strideX, offsetX, y, strideY, offsetY )
Multiplies x
by a constant alpha
and adds the result to y
using alternative indexing semantics.
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var y = [ 1.0, 1.0, 1.0, 1.0, 1.0 ];
var alpha = 5.0;
gaxpy.ndarray( x.length, alpha, x, 1, 0, y, 1, 0 );
// y => [ 6.0, 11.0, 16.0, 21.0, 26.0 ]
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 offsetX
and offsetY
parameters support indexing semantics based on starting indices. For example, to multiply every other value in x
by a constant alpha
starting from the second value and add to the last N
elements in y
where x[i] -> y[n]
, x[i+2] -> y[n-1]
,...,
var floor = require( '@stdlib/math/base/special/floor' );
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];
var alpha = 5.0;
var N = floor( x.length / 2 );
gaxpy.ndarray( N, alpha, x, 2, 1, y, -1, y.length-1 );
// y => [ 7.0, 8.0, 9.0, 40.0, 31.0, 22.0 ]
Notes
- If
N <= 0
oralpha == 0
, both functions returny
unchanged. gaxpy()
corresponds to the BLAS level 1 functiondaxpy
with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (daxpy
,saxpy
, etc.) are likely to be significantly more performant.
Examples
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var gaxpy = require( '@stdlib/blas/base/gaxpy' );
var x;
var y;
var i;
x = [];
y = [];
for ( i = 0; i < 10; i++ ) {
x.push( round( randu()*100.0 ) );
y.push( round( randu()*10.0 ) );
}
console.log( x );
console.log( y );
gaxpy.ndarray( x.length, 5.0, x, 1, 0, y, -1, y.length-1 );
console.log( y );