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# csum

> Calculate the sum of single-precision complex floating-point strided array elements.

<section class="intro">

</section>

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<section class="usage">

## Usage

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

#### csum( N, x, strideX )

Computes the sum of single-precision complex floating-point strided array elements.

```javascript
var Complex64Array = require( '@stdlib/array/complex64' );

var x = new Complex64Array( [ 1.0, -2.0, 2.0, 3.0 ] );

var v = csum( x.length, x, 1 );
// returns <Complex64>[ 3.0, 1.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **x**: input [`Complex64Array`][@stdlib/array/complex64].
-   **strideX**: stride length for `x`.

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

```javascript
var Complex64Array = require( '@stdlib/array/complex64' );

var x = new Complex64Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );

var v = csum( 2, x, 2 );
// returns <Complex64>[ -1.0, 5.0 ]
```

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 Complex64Array = require( '@stdlib/array/complex64' );

var x0 = new Complex64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Complex64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = csum( 2, x1, 2 );
// returns <Complex64>[ 5.0, 2.0 ]
```

#### csum.ndarray( N, x, strideX, offsetX )

Computes the sum of single-precision complex floating-point strided array elements using alternative indexing semantics.

```javascript
var Complex64Array = require( '@stdlib/array/complex64' );

var x = new Complex64Array( [ 1.0, -2.0, 2.0, 3.0 ] );

var v = csum.ndarray( 2, x, 1, 0 );
// returns <Complex64>[ 3.0, 1.0 ]
```

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 calculate the sum of every other element starting from the second element:

```javascript
var Complex64Array = require( '@stdlib/array/complex64' );

var x = new Complex64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );

var v = csum.ndarray( 2, x, 2, 1 );
// returns <Complex64>[ 5.0, 2.0 ]
```

</section>

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<section class="notes">

## Notes

-   If `N <= 0`, both functions return `0.0 + 0.0i`.

</section>

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<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var Complex64Array = require( '@stdlib/array/complex64' );
var csum = require( '@stdlib/blas/ext/base/csum' );

var xbuf = discreteUniform( 10, -100, 100, {
    'dtype': 'float32'
});
console.log( xbuf );

var x = new Complex64Array( xbuf );
var v = csum( x.length, x, 1 );
console.log( v );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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<section class="intro">

</section>

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<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/blas/ext/base/csum.h"
```

#### stdlib_strided_csum( N, \*X, strideX )

Computes the sum of single-precision complex floating-point strided array elements.

```c
#include "stdlib/complex/float32/ctor.h"

const stdlib_complex64_t x[] = {
    stdlib_complex64( 1.0f, 2.0f ),
    stdlib_complex64( 3.0f, 4.0f )
};

stdlib_complex64_t v = stdlib_strided_csum( 2, x, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] stdlib_complex64_t*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.

```c
stdlib_complex64_t stdlib_strided_csum( const CBLAS_INT N, const stdlib_complex64_t *X, const CBLAS_INT strideX );
```

#### stdlib_strided_csum_ndarray( N, \*X, strideX, offsetX )

Computes the sum of single-precision complex floating-point strided array elements using alternative indexing semantics.

```c
#include "stdlib/complex/float32/ctor.h"

const stdlib_complex64_t x[] = {
    stdlib_complex64( 1.0f, 2.0f ),
    stdlib_complex64( 3.0f, 4.0f )
};

stdlib_complex64_t v = stdlib_strided_csum_ndarray( 2, x, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] stdlib_complex64_t*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.

```c
stdlib_complex64_t stdlib_strided_csum_ndarray( const CBLAS_INT N, const stdlib_complex64_t *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
```

</section>

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<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

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<!-- C API usage examples. -->

<section class="examples">

### Examples

```c
#include "stdlib/blas/ext/base/csum.h"
#include "stdlib/complex/float32/ctor.h"
#include "stdlib/complex/float32/real.h"
#include "stdlib/complex/float32/imag.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    const stdlib_complex64_t x[] = {
        stdlib_complex64( 1.0f, 2.0f ),
        stdlib_complex64( 3.0f, 4.0f ),
        stdlib_complex64( 5.0f, 6.0f ),
        stdlib_complex64( 7.0f, 8.0f )
    };

    // Specify the number of elements:
    const int N = 4;

    // Specify the stride length:
    const int strideX = 1;

    // Compute the sum:
    stdlib_complex64_t v = stdlib_strided_csum( N, x, strideX );

    // Print the result:
    printf( "sum: %f + %fi\n", stdlib_complex64_real( v ), stdlib_complex64_imag( v ) );
}
```

</section>

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</section>

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<section class="references">

</section>

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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

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</section>

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<section class="links">

[@stdlib/array/complex64]: https://www.npmjs.com/package/@stdlib/array-complex64

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

</section>

<!-- /.links -->
