README
dscal
Multiply a double-precision floating-point vector
x
by a constantalpha
.
Installation
npm install @stdlib/blas-base-dscal
Usage
var dscal = require( '@stdlib/blas-base-dscal' );
dscal( N, alpha, x, stride )
Multiplies a double-precision floating-point vector x
by a constant alpha
.
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dscal( x.length, 5.0, x, 1 );
// x => <Float64Array>[ -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
Float64Array
. - 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 Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var N = floor( x.length / 2 );
dscal( N, 5.0, x, 2 );
// x => <Float64Array>[ -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 = 3;
// Scale every other value...
dscal( N, 5.0, x1, 2 );
// 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.
dscal.ndarray( N, alpha, x, stride, offset )
Multiplies a double-precision floating-point vector x
by a constant alpha
using alternative indexing semantics.
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float64Array>[ -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 Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
dscal.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float64Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]
Notes
Examples
var round = require( '@stdlib/math-base-special-round' );
var randu = require( '@stdlib/random-base-randu' );
var Float64Array = require( '@stdlib/array-float64' );
var dscal = require( '@stdlib/blas-base-dscal' );
var rand;
var sign;
var x;
var i;
x = new Float64Array( 10 );
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 );
dscal( x.length, 5.0, x, 1 );
console.log( x );
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.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2021. The Stdlib Authors.