dssumpw
Calculate the sum of single-precision floating-point strided array elements using pairwise summation with extended accumulation and returning an extended precision result.
Usage
var dssumpw = require( '@stdlib/blas/ext/base/dssumpw' );
dssumpw( N, x, strideX )
Computes the sum of single-precision floating-point strided array elements using pairwise summation with extended accumulation and returning an extended precision result.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var v = dssumpw( x.length, x, 1 );
// returns 1.0
The function has the following parameters:
- N: number of indexed elements.
- x: input
Float32Array. - strideX: stride length for
x.
The N and stride parameters determine which elements in x are accessed at runtime. For example, to compute the sum of every other element:
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var v = dssumpw( 4, x, 2 );
// returns 5.0
Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float32Array = require( '@stdlib/array/float32' );
var x0 = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var v = dssumpw( 4, x1, 2 );
// returns 5.0
dssumpw.ndarray( N, x, strideX, offsetX )
Computes the sum of single-precision floating-point strided array elements using pairwise summation with extended accumulation and alternative indexing semantics and returning an extended precision result.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var v = dssumpw.ndarray( x.length, x, 1, 0 );
// returns 1.0
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 calculate the sum of every other element starting from the second element:
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var v = dssumpw.ndarray( 4, x, 2, 1 );
// returns 5.0
Notes
- If
N <= 0, both functions return0.0. - Accumulated intermediate values are stored as double-precision floating-point numbers.
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var dssumpw = require( '@stdlib/blas/ext/base/dssumpw' );
var x = discreteUniform( 10, -100, 100, {
'dtype': 'float32'
});
console.log( x );
var v = dssumpw( x.length, x, 1 );
console.log( v );
C APIs
Usage
#include "stdlib/blas/ext/base/dssumpw.h"
stdlib_strided_dssumpw( N, *X, strideX )
Computes the sum of single-precision floating-point strided array elements using pairwise summation with extended accumulation and returning an extended precision result.
const float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
double v = stdlib_strided_dssumpw( 4, x, 1 );
// returns 10.0
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*input array. - strideX:
[in] CBLAS_INTstride length forX.
double stdlib_strided_dssumpw( const CBLAS_INT N, const float *X, const CBLAS_INT strideX );
stdlib_strided_dssumpw_ndarray( N, *X, strideX, offsetX )
Computes the sum of single-precision floating-point strided array elements using pairwise summation with extended accumulation and alternative indexing semantics and returning an extended precision result.
const float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
double v = stdlib_strided_dssumpw_ndarray( 4, x, 1, 0 );
// returns 10.0
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*input array. - strideX:
[in] CBLAS_INTstride length forX. - offsetX:
[in] CBLAS_INTstarting index forX.
double stdlib_strided_dssumpw_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
Examples
#include "stdlib/blas/ext/base/dssumpw.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
const float x[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f, 7.0f, 8.0f };
// Specify the number of elements:
const int N = 5;
// Specify the stride length:
const int strideX = 2;
// Compute the sum:
double v = stdlib_strided_dssumpw( N, x, strideX );
// Print the result:
printf( "sum: %lf\n", v );
}
References
- Higham, Nicholas J. 1993. "The Accuracy of Floating Point Summation." SIAM Journal on Scientific Computing 14 (4): 783–99. doi:10.1137/0914050.