dapxsumkbn2
Add a scalar constant to each double-precision floating-point strided array element and compute the sum using a second-order iterative Kahan–Babuška algorithm.
Usage
var dapxsumkbn2 = require( '@stdlib/blas/ext/base/dapxsumkbn2' );
dapxsumkbn2( N, alpha, x, strideX )
Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using a second-order iterative Kahan–Babuška algorithm.
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var v = dapxsumkbn2( 3, 5.0, x, 1 );
// returns 16.0
The function has the following parameters:
- N: number of indexed elements.
- x: input
Float64Array
. - strideX: index increment for
x
.
The N
and stride parameters determine which elements in the strided array are accessed at runtime. For example, to access every other element in x
,
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var v = dapxsumkbn2( 4, 5.0, x, 2 );
// returns 25.0
Note that indexing is relative to the first index. To introduce an offset, use typed array
views.
var Float64Array = require( '@stdlib/array/float64' );
var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var v = dapxsumkbn2( 4, 5.0, x1, 2 );
// returns 25.0
dapxsumkbn2.ndarray( N, alpha, x, strideX, offsetX )
Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using a second-order iterative Kahan–Babuška algorithm and alternative indexing semantics.
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var v = dapxsumkbn2.ndarray( 3, 5.0, x, 1, 0 );
// returns 16.0
The function has the following additional parameters:
- offsetX: starting index for
x
.
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 every other value in x
starting from the second value
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var v = dapxsumkbn2.ndarray( 4, 5.0, x, 2, 1 );
// returns 25.0
Notes
- If
N <= 0
, both functions return0.0
.
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var dapxsumkbn2 = require( '@stdlib/blas/ext/base/dapxsumkbn2' );
var x = discreteUniform( 10, -100, 100, {
'dtype': 'float64'
});
console.log( x );
var v = dapxsumkbn2( x.length, 5.0, x, 1 );
console.log( v );
C APIs
Usage
#include "stdlib/blas/ext/base/dapxsumkbn2.h"
stdlib_strided_dapxsumkbn2( N, alpha, *X, strideX )
Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using a second-order iterative Kahan–Babuška algorithm.
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
double v = stdlib_strided_dapxsumkbn2( 4, 5.0, x, 1 );
// returns 30.0
The function accepts the following arguments:
- N:
[in] CBLAS_INT
number of indexed elements. - alpha:
[in] double
scalar constant. - X:
[in] double*
input array. - strideX:
[in] CBLAS_INT
index increment forX
.
double stdlib_strided_dapxsumkbn2( const CBLAS_INT N, const double alpha, const double *X, const CBLAS_INT strideX );
stdlib_strided_dapxsumkbn2_ndarray( N, alpha, *X, strideX, offsetX )
Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using a second-order iterative Kahan–Babuška algorithm and alternative indexing semantics.
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
double v = stdlib_strided_dapxsumkbn2_ndarray( 4, 5.0, x, 1, 0 );
// returns 30.0
The function accepts the following arguments:
- N:
[in] CBLAS_INT
number of indexed elements. - alpha:
[in] double
scalar constant. - X:
[in] double*
input array. - strideX:
[in] CBLAS_INT
index increment forX
. - offsetX:
[in] CBLAS_INT
starting index forX
.
double stdlib_strided_dapxsumkbn2_ndarray( const CBLAS_INT N, const double alpha, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
Examples
#include "stdlib/blas/ext/base/dapxsumkbn2.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
const 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;
// Compute the sum:
double v = stdlib_strided_dapxsumkbn2( N, 5.0, x, strideX );
// Print the result:
printf( "Sum: %lf\n", sum );
}
References
- Klein, Andreas. 2005. "A Generalized Kahan-Babuška-Summation-Algorithm." Computing 76 (3): 279–93. doi:10.1007/s00607-005-0139-x.