@stdlib/blas-ext-base-dcusum
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Calculate the cumulative sum of double-precision floating-point strided array elements.
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# dcusum
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> Calculate the cumulative sum of double-precision floating-point strided array elements.
<section class="intro">
</section>
<!-- /.intro -->
<section class="installation">
## Installation
```bash
npm install @stdlib/blas-ext-base-dcusum
```
</section>
<section class="usage">
## Usage
```javascript
var dcusum = require( '@stdlib/blas-ext-base-dcusum' );
```
#### dcusum( N, sum, x, strideX, y, strideY )
Computes the cumulative sum of double-precision floating-point strided array elements.
```javascript
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var y = new Float64Array( x.length );
dcusum( x.length, 0.0, x, 1, y, 1 );
// y => <Float64Array>[ 1.0, -1.0, 1.0 ]
x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
y = new Float64Array( x.length );
dcusum( x.length, 10.0, x, 1, y, 1 );
// y => <Float64Array>[ 11.0, 9.0, 11.0 ]
```
The function has the following parameters:
- **N**: number of indexed elements.
- **sum**: initial sum.
- **x**: input [`Float64Array`][@stdlib/array/float64].
- **strideX**: index increment for `x`.
- **y**: output [`Float64Array`][@stdlib/array/float64].
- **strideY**: index increment for `y`.
The `N` and `stride` parameters determine which elements in the strided arrays are accessed at runtime. For example, to compute the cumulative sum of every other element in the strided input array,
```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 y = new Float64Array( x.length );
var v = dcusum( 4, 0.0, x, 2, y, 1 );
// y => <Float64Array>[ 1.0, 3.0, 1.0, 5.0, 0.0, 0.0, 0.0, 0.0 ]
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
<!-- eslint-disable stdlib/capitalized-comments -->
```javascript
var Float64Array = require( '@stdlib/array-float64' );
// Initial arrays...
var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var y0 = new Float64Array( x0.length );
// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
dcusum( 4, 0.0, x1, -2, y1, 1 );
// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 4.0, 6.0, 4.0, 5.0, 0.0 ]
```
#### dcusum.ndarray( N, sum, x, strideX, offsetX, y, strideY, offsetY )
Computes the cumulative sum of double-precision floating-point strided array elements using alternative indexing semantics.
```javascript
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ 1.0, -2.0, 2.0 ] );
var y = new Float64Array( x.length );
dcusum.ndarray( x.length, 0.0, x, 1, 0, y, 1, 0 );
// y => <Float64Array>[ 1.0, -1.0, 1.0 ]
```
The function has the following additional parameters:
- **offsetX**: starting index for `x`.
- **offsetY**: starting index for `y`.
While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, `offsetX` and `offsetY` parameters support indexing semantics based on a starting indices. For example, to calculate the cumulative sum of every other value in the strided input array starting from the second value and to store in the last `N` elements of the strided output array starting from the last 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 y = new Float64Array( x.length );
dcusum.ndarray( 4, 0.0, x, 2, 1, y, -1, y.length-1 );
// y => <Float64Array>[ 0.0, 0.0, 0.0, 0.0, 5.0, 1.0, -1.0, 1.0 ]
```
</section>
<!-- /.usage -->
<section class="notes">
## Notes
- If `N <= 0`, both functions return `y` unchanged.
</section>
<!-- /.notes -->
<section class="examples">
## Examples
<!-- eslint no-undef: "error" -->
```javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var filledarrayBy = require( '@stdlib/array-filled-by' );
var Float64Array = require( '@stdlib/array-float64' );
var dcusum = require( '@stdlib/blas-ext-base-dcusum' );
var x = filledarrayBy( 10, 'float64', discreteUniform( 0, 100 ) );
var y = new Float64Array( x.length );
console.log( x );
console.log( y );
dcusum( x.length, 0.0, x, 1, y, -1 );
console.log( y );
```
</section>
<!-- /.examples -->
<section class="references">
</section>
<!-- /.references -->
<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
<section class="related">
* * *
## See Also
- <span class="package-name">[`@stdlib/blas-ext/base/dcusumpw`][@stdlib/blas/ext/base/dcusumpw]</span><span class="delimiter">: </span><span class="description">calculate the cumulative sum of double-precision floating-point strided array elements using pairwise summation.</span>
- <span class="package-name">[`@stdlib/blas-ext/base/gcusum`][@stdlib/blas/ext/base/gcusum]</span><span class="delimiter">: </span><span class="description">calculate the cumulative sum of strided array elements.</span>
- <span class="package-name">[`@stdlib/blas-ext/base/scusum`][@stdlib/blas/ext/base/scusum]</span><span class="delimiter">: </span><span class="description">calculate the cumulative sum of single-precision floating-point strided array elements.</span>
</section>
<!-- /.related -->
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<section class="main-repo" >
* * *
## Notice
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
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---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].
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[@stdlib/array/float64]: https://www.npmjs.com/package/@stdlib/array-float64
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
<!-- <related-links> -->
[@stdlib/blas/ext/base/dcusumpw]: https://www.npmjs.com/package/@stdlib/blas-ext-base-dcusumpw
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