Usage

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

#### dapxsumpw( N, alpha, x, strideX )

Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using pairwise summation.

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

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

var v = dapxsumpw( x.length, 5.0, x, 1 );
// returns 16.0
`

The function has the following parameters:

- N: number of indexed elements.
- x: input [Float64Array][@stdlib/array/float64].
- strideX: stride length 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:

`javascript
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 = dapxsumpw( 4, 5.0, x, 2 );
// returns 25.0
`

Note that indexing is relative to the first index. To introduce an offset, use [typed array][mdn-typed-array] views.

`javascript
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 = dapxsumpw( 4, 5.0, x1, 2 );
// returns 25.0
`

#### dapxsumpw.ndarray( N, alpha, x, strideX, offsetX )

Adds a scalar constant to each double-precision floating-point strided array element and computes the sum using pairwise summation and alternative indexing semantics.

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

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

var v = dapxsumpw.ndarray( x.length, 5.0, x, 1, 0 );
// returns 16.0
`

The function has the following additional parameters:

- offsetX: starting index for x.

While [typed array][mdn-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 element starting from the second element:

`javascript
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 = dapxsumpw.ndarray( 4, 5.0, x, 2, 1 );
// returns 25.0
`