dapx
Add a constant to each element in a double-precision floating-point strided array.
Usage
var dapx = require( '@stdlib/blas/ext/base/dapx' );
dapx( N, alpha, x, strideX )
Adds a scalar constant alpha
to each element in a double-precision floating-point strided array.
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 ] );
dapx( x.length, 5.0, x, 1 );
// x => <Float64Array>[ 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
Float64Array
. - strideX: 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 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 ] );
dapx( 4, 5.0, x, 2 );
// x => <Float64Array>[ 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 Float64Array = require( '@stdlib/array/float64' );
// 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
// Add a constant to every other element...
dapx( 3, 5.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]
dapx.ndarray( N, alpha, x, strideX, offsetX )
Adds a scalar constant alpha
to each element in a double-precision floating-point strided array 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 ] );
dapx.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float64Array>[ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]
The function has the following additional parameters:
- offsetX: 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 Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
dapx.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float64Array>[ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]
Notes
- If
N <= 0
, both functions return the strided array unchanged.
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var dapx = require( '@stdlib/blas/ext/base/dapx' );
var x = discreteUniform( 10, -100, 100, {
'dtype': 'float64'
});
console.log( x );
dapx( x.length, 5.0, x, 1 );
console.log( x );
C APIs
Usage
#include "stdlib/blas/ext/base/dapx.h"
c_dapx( N, alpha, *X, strideX )
Adds a scalar constant alpha
to each element in a double-precision floating-point strided array.
double x[] = { 1.0, 2.0, 3.0, 4.0 };
c_dapx( 4, 5.0, x, 1 );
The function accepts the following arguments:
- N:
[in] CBLAS_INT
number of indexed elements. - alpha:
[in] double
scalar constant. - X:
[inout] double*
input array. - strideX:
[in] CBLAS_INT
index increment forX
.
void c_dapx( const CBLAS_INT N, const double alpha, double *X, const CBLAS_INT strideX );
c_dapx_ndarray( N, alpha, *X, strideX, offsetX )
Adds a scalar constant alpha
to each element in a double-precision floating-point strided array X
using alternative indexing semantics.
double x[] = { 1.0, 2.0, 3.0, 4.0 };
c_dapx_ndarray( 4, 5.0, x, 1, 0 );
The function accepts the following arguments:
- N:
[in] CBLAS_INT
number of indexed elements. - alpha:
[in] double
scalar constant. - X:
[inout] double*
input array. - strideX:
[in] CBLAS_INT
index increment forX
. - offsetX:
[in] CBLAS_INT
starting index forX
.
void c_dapx_ndarray( const CBLAS_INT N, const double alpha, double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
Examples
#include "stdlib/blas/ext/base/dapx.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 7.0, -8.0 };
// Specify the number of indexed elements:
const int N = 8;
// Specify a stride:
const int strideX = 1;
// Fill the array:
c_dapx( N, 5.0, x, strideX );
// Print the result:
for ( int i = 0; i < 8; i++ ) {
printf( "x[ %i ] = %lf\n", i, x[ i ] );
}
}