sscal

Multiply a single-precision floating-point vector x by a constant alpha.

Usage

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

sscal( N, alpha, x, stride )

Multiplies a single-precision floating-point vector x by a constant alpha.

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

sscal( x.length, 5.0, x, 1 );
// x => <Float32Array>[ -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 Float32Array.
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 Float32Array = require( '@stdlib/array/float32' );
var floor = require( '@stdlib/math/base/special/floor' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

var N = floor( x.length / 2 );

sscal( N, 5.0, x, 2 );
// x => <Float32Array>[ -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 Float32Array = require( '@stdlib/array/float32' );
var floor = require( '@stdlib/math/base/special/floor' );

// Initial array...
var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = 3;

// Scale every other value...
sscal( N, 5.0, x1, 2 );
// x0 => <Float32Array>[ 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.

sscal.ndarray( N, alpha, x, stride, offset )

Multiplies a single-precision floating-point vector x by a constant alpha using alternative indexing semantics.

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

sscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float32Array>[ -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 Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

sscal.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]

Notes

If N <= 0, both functions return x unchanged.
sscal() corresponds to the BLAS level 1 function sscal.

Examples

var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var Float32Array = require( '@stdlib/array/float32' );
var sscal = require( '@stdlib/blas/base/sscal' );

var rand;
var sign;
var x;
var i;

x = new Float32Array( 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 );

sscal( x.length, 5.0, x, 1 );
console.log( x );