gscal
Multiply a vector
x
by a constantalpha
.
Usage
var gscal = require( '@stdlib/blas/base/gscal' );
gscal( N, alpha, x, stride )
Multiplies a vector x
by a constant alpha
.
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
gscal( x.length, 5.0, x, 1 );
// x => [ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]
The function has the following parameters:
- N: number of indexed elements.
- alpha: scalar constant.
- x: input
Array
ortyped array
. - stride: index increment.
The N
and stride
parameters determine which elements in x
are accessed at runtime. For example, to multiply every other value by a constant
var floor = require( '@stdlib/math/base/special/floor' );
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
var N = floor( x.length / 2 );
var alpha = 5.0;
var stride = 2;
gscal( N, alpha, x, stride );
// x => [ -10.0, 1.0, 15.0, -5.0, 20.0, 0.0, -5.0, -3.0 ]
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 array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length / 2 );
var alpha = 5.0;
var stride = 2;
// Scale every other value...
gscal( N, alpha, x1, stride );
// x0 => <Float64Array>[ 1.0, -10.0, 3.0, -20.0, 5.0, -30.0 ]
If either N
or stride
is less than or equal to 0
, the function returns x
unchanged.
gscal.ndarray( N, alpha, x, stride, offset )
Multiplies a vector x
by a constant alpha
using alternative indexing semantics.
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
gscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => [ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]
The function has the following additional parameters:
- offset: starting index.
While typed array
views mandate a view offset based on the underlying buffer
, the offset
parameter supports indexing semantics based on a starting index. For example, to multiply the last three elements of x
by a constant
var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
var alpha = 5.0;
gscal.ndarray( 3, alpha, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]
Notes
- If
N <= 0
, both functions returnx
unchanged. gscal()
corresponds to the BLAS level 1 functiondscal
with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (dscal
,sscal
, etc.) are likely to be significantly more performant.
Examples
var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var Float64Array = require( '@stdlib/array/float64' );
var gscal = require( '@stdlib/blas/base/gscal' );
var rand;
var sign;
var x;
var i;
x = new Float64Array( 100 );
for ( i = 0; i < x.length; i++ ) {
rand = round( randu()*100.0 );
sign = randu();
if ( sign < 0.5 ) {
sign = -1.0;
} else {
sign = 1.0;
}
x[ i ] = sign * rand;
}
console.log( x );
gscal( x.length, 5.0, x, 1 );
console.log( x );