# @stdlib/blas-ext-base-ssumkbn2

Calculate the sum of single-precision floating-point strided array elements using a second-order iterative Kahan–Babuška algorithm.

## Usage no npm install needed!

``````<script type="module">
import stdlibBlasExtBaseSsumkbn2 from 'https://cdn.skypack.dev/@stdlib/blas-ext-base-ssumkbn2';
</script>``````

# ssumkbn2

Calculate the sum of single-precision floating-point strided array elements using a second-order iterative Kahan–Babuška algorithm.

## Installation

``````npm install @stdlib/blas-ext-base-ssumkbn2
``````

## Usage

``````var ssumkbn2 = require( '@stdlib/blas-ext-base-ssumkbn2' );
``````

#### ssumkbn2( N, x, stride )

Computes the sum of single-precision floating-point strided array elements using a second-order iterative Kahan–Babuška algorithm.

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

var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var N = x.length;

var v = ssumkbn2( 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 Float32Array = require( '@stdlib/array-float32' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var N = floor( x.length / 2 );

var v = ssumkbn2( N, 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 floor = require( '@stdlib/math-base-special-floor' );

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 N = floor( x0.length / 2 );

var v = ssumkbn2( N, x1, 2 );
// returns 5.0
``````

#### ssumkbn2.ndarray( N, x, stride, offset )

Computes the sum of single-precision floating-point strided array elements using a second-order iterative Kahan–Babuška algorithm and alternative indexing semantics.

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

var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var N = x.length;

var v = ssumkbn2.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 Float32Array = require( '@stdlib/array-float32' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var N = floor( x.length / 2 );

var v = ssumkbn2.ndarray( N, x, 2, 1 );
// returns 5.0
``````

## Notes

• If `N <= 0`, both functions return `0.0`.

## Examples

``````var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var Float32Array = require( '@stdlib/array-float32' );
var ssumkbn2 = require( '@stdlib/blas-ext-base-ssumkbn2' );

var x;
var i;

x = new Float32Array( 10 );
for ( i = 0; i < x.length; i++ ) {
x[ i ] = round( randu()*100.0 );
}
console.log( x );

var v = ssumkbn2( x.length, x, 1 );
console.log( v );
``````

## References

• Klein, Andreas. 2005. "A Generalized Kahan-Babuška-Summation-Algorithm." Computing 76 (3): 279–93. doi:10.1007/s00607-005-0139-x.

## 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.