sapx

Add a constant to each element in a single-precision floating-point strided array.

Usage

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

sapx( N, alpha, x, stride )

Adds a constant alpha to each element in a single-precision floating-point strided array x.

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 ] );

sapx( x.length, 5.0, x, 1 );
// x => <Float32Array>[ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]

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 the strided array are accessed at runtime. For example, to add a constant to every other element

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 ] );

sapx( 4, 5.0, x, 2 );
// x => <Float32Array>[ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -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' );

// 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

// Add a constant to every other element...
sapx( 3, 5.0, x1, 2 );
// x0 => <Float32Array>[ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]

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

Adds a constant alpha to each element in a single-precision floating-point strided array x 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 ] );

sapx.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float32Array>[ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]

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 access only the last three elements of the strided array

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

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

sapx.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]

Notes

If N <= 0, both functions return the input array unchanged.

Examples

var uniform = require( '@stdlib/random/base/uniform' ).factory;
var filledarrayBy = require( '@stdlib/array/filled-by' );
var sapx = require( '@stdlib/blas/ext/base/sapx' );

var x = filledarrayBy( 10, 'float32', uniform( -100.0, 100.0 ) );
console.log( x );

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