# @stdlib/blas-ext-base-dsumkbn

Calculate the sum of double-precision floating-point strided array elements using an improved Kahan–Babuška algorithm.

## Usage no npm install needed!

``````<script type="module">
import stdlibBlasExtBaseDsumkbn from 'https://cdn.skypack.dev/@stdlib/blas-ext-base-dsumkbn';
</script>``````

# dsumkbn

Calculate the sum of double-precision floating-point strided array elements using an improved Kahan–Babuška algorithm.

## Installation

``````npm install @stdlib/blas-ext-base-dsumkbn
``````

## Usage

``````var dsumkbn = require( '@stdlib/blas-ext-base-dsumkbn' );
``````

#### dsumkbn( N, x, stride )

Computes the sum of double-precision floating-point strided array elements using an improved Kahan–Babuška algorithm.

``````var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var N = x.length;

var v = dsumkbn( N, x, 1 );
// returns 1.0
``````

The function has the following parameters:

The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to compute the sum of every other element in `x`,

``````var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float64Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var N = floor( x.length / 2 );

var v = dsumkbn( N, x, 2 );
// returns 5.0
``````

Note that indexing is relative to the first index. To introduce an offset, use `typed array` views.

``````var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

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 N = floor( x0.length / 2 );

var v = dsumkbn( N, x1, 2 );
// returns 5.0
``````

#### dsumkbn.ndarray( N, x, stride, offset )

Computes the sum of double-precision floating-point strided array elements using an improved Kahan–Babuška algorithm and alternative indexing semantics.

``````var Float64Array = require( '@stdlib/array-float64' );

var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var N = x.length;

var v = dsumkbn.ndarray( N, x, 1, 0 );
// returns 1.0
``````

The function has the following additional parameters:

• offset: 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 value in `x` starting from the second value

``````var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var N = floor( x.length / 2 );

var v = dsumkbn.ndarray( N, x, 2, 1 );
// returns 5.0
``````

## Examples

``````var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var Float64Array = require( '@stdlib/array-float64' );
var dsumkbn = require( '@stdlib/blas-ext-base-dsumkbn' );

var x;
var i;

x = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
x[ i ] = round( randu()*100.0 );
}
console.log( x );

var v = dsumkbn( x.length, x, 1 );
console.log( v );
``````

## Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

#### Community 