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# dediff

> Calculate the differences between consecutive elements of a double-precision floating-point strided array.

<section class="usage">

## Usage

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

<!-- lint disable maximum-heading-length -->

#### dediff( N, x, strideX, N1, prepend, strideP, N2, append, strideA, out, strideOut )

<!-- lint enable maximum-heading-length -->

Calculates the differences between consecutive elements of a double-precision floating-point strided array.

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

var x = new Float64Array( [ 2.0, 4.0, 6.0, 8.0, 10.0 ] );
var p = new Float64Array( [ 1.0 ] );
var a = new Float64Array( [ 11.0 ] );
var out = new Float64Array( 6 );

dediff( x.length, x, 1, 1, p, 1, 1, a, 1, out, 1 );
// out => <Float64Array>[ 1.0, 2.0, 2.0, 2.0, 2.0, 11.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **x**: input [`Float64Array`][@stdlib/array/float64].
-   **strideX**: stride length for `x`.
-   **N1**: number of indexed elements to `prepend`.
-   **prepend**: a [`Float64Array`][@stdlib/array/float64] containing values to prepend after computing differences.
-   **strideP**: stride length for `prepend`.
-   **N2**: number of indexed elements to `append`.
-   **append**: a [`Float64Array`][@stdlib/array/float64] containing values to append after computing differences.
-   **strideA**: stride length for `append`.
-   **out**: output [`Float64Array`][@stdlib/array/float64]. Must have `N + N1 + N2 - 1` indexed elements.
-   **strideOut**: stride length for `out`.

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

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

var x = new Float64Array( [ 2.0, 4.0, 6.0, 8.0, 10.0 ] );
var p = new Float64Array( [ 1.0 ] );
var a = new Float64Array( [ 11.0 ] );
var out = new Float64Array( 4 );

dediff( 3, x, 2, 1, p, 1, 1, a, 1, out, 1 );
// out => <Float64Array>[ 1.0, 4.0, 4.0, 11.0 ]
```

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' );

// Initial array...
var x0 = new Float64Array( [ 2.0, 4.0, 6.0, 8.0, 10.0 ] );

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var p = new Float64Array( [ 1.0 ] );
var a = new Float64Array( [ 11.0 ] );
var out = new Float64Array( 5 );

dediff( x1.length, x1, 1, 1, p, 1, 1, a, 1, out, 1 );
// out => <Float64Array>[ 1.0, 2.0, 2.0, 2.0, 11.0 ]
```

<!-- lint disable maximum-heading-length -->

#### dediff.ndarray( N, x, strideX, offsetX, N1, prepend, strideP, offsetP, N2, append, strideA, offsetA, out, strideOut, offsetOut )

<!-- lint enable maximum-heading-length -->

Calculates the differences between consecutive elements of a double-precision floating-point strided array using alternative indexing semantics.

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

var x = new Float64Array( [ 2.0, 4.0, 6.0, 8.0, 10.0 ] );
var p = new Float64Array( [ 1.0 ] );
var a = new Float64Array( [ 11.0 ] );
var out = new Float64Array( 6 );

dediff.ndarray( x.length, x, 1, 0, 1, p, 1, 0, 1, a, 1, 0, out, 1, 0 );
// out => <Float64Array>[ 1.0, 2.0, 2.0, 2.0, 2.0, 11.0 ]
```

The function has the following additional parameters:

-   **offsetX**: starting index for `x`.
-   **offsetP**: starting index for `prepend`.
-   **offsetA**: starting index for `append`.
-   **offsetOut**: starting index for `out`.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, offset parameters support indexing semantics based on starting indices. For example, to access only the last three elements:

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

var x = new Float64Array( [ 2.0, 4.0, 6.0, 8.0, 10.0 ] );
var p = new Float64Array( [ 1.0 ] );
var a = new Float64Array( [ 11.0 ] );
var out = new Float64Array( 4 );

dediff.ndarray( 3, x, 1, x.length-3, 1, p, 1, 0, 1, a, 1, 0, out, 1, 0 );
// out => <Float64Array>[ 1.0, 2.0, 2.0, 11.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N + N1 + N2 <= 1`, both functions return the output array unchanged.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var Float64Array = require( '@stdlib/array/float64' );
var dediff = require( '@stdlib/blas/ext/base/dediff' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float64'
});
console.log( 'Input array:', x );

var p = discreteUniform( 2, -100, 100, {
    'dtype': 'float64'
});
console.log( 'Prepend array:', p );

var a = discreteUniform( 2, -100, 100, {
    'dtype': 'float64'
});
console.log( 'Append array:', a );

var out = new Float64Array( 13 );

dediff( x.length, x, 1, 2, p, 1, 2, a, 1, out, 1 );
console.log( 'Output:', out );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

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

<!-- lint disable maximum-heading-length -->

#### stdlib_strided_dediff( N, \*X, strideX, N1, \*Prepend, strideP, N2, \*Append, strideA, \*Out, strideOut )

<!-- lint enable maximum-heading-length -->

Calculates the differences between consecutive elements of a double-precision floating-point strided array.

```c
const double x[] = { 2.0, 4.0, 6.0, 8.0, 10.0 };
const double p[] = { 1.0 };
const double a[] = { 11.0 };
double out[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

stdlib_strided_dediff( 5, x, 1, 1, p, 1, 1, a, 1, out, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] double` input [`Float64Array`][@stdlib/array/float64].
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
-   **N1**: `[in] CBLAS_INT` number of indexed elements to prepend.
-   **Prepend**: `[in] double` a [`Float64Array`][@stdlib/array/float64] containing values to prepend after computing differences.
-   **strideP**: `[in] CBLAS_INT` stride length for `Prepend`.
-   **N2**: `[in] CBLAS_INT` number of indexed elements to append.
-   **Append**: `[in] double` a [`Float64Array`][@stdlib/array/float64] containing values to append after computing differences.
-   **strideA**: `[in] CBLAS_INT` stride length for `Append`.
-   **Out**: `[out] double` output [`Float64Array`][@stdlib/array/float64]. Must have `N + N1 + N2 - 1` indexed elements.
-   **strideOut**: `[in] CBLAS_INT` stride length for `Out`.

```c
void stdlib_strided_dediff( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const CBLAS_INT N1, const double *Prepend, const CBLAS_INT strideP, const CBLAS_INT N2, const double *Append, const CBLAS_INT strideA, double *Out, const CBLAS_INT strideOut );
```

<!-- lint disable maximum-heading-length -->

#### stdlib_strided_dediff_ndarray( N, \*X, strideX, offsetX, N1, \*Prepend, strideP, offsetP, N2, \*Append, strideA, offsetA, \*Out, strideOut, offsetOut )

<!-- lint enable maximum-heading-length -->

Calculates the differences between consecutive elements of a double-precision floating-point strided array using alternative indexing semantics.

```c
const double x[] = { 2.0, 4.0, 6.0, 8.0, 10.0 };
const double p[] = { 1.0 };
const double a[] = { 11.0 };
double out[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

stdlib_strided_dediff_ndarray( 5, x, 1, 0, 1, p, 1, 0, 1, a, 1, 0, out, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] double` input [`Float64Array`][@stdlib/array/float64].
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.
-   **N1**: `[in] CBLAS_INT` number of indexed elements to prepend.
-   **Prepend**: `[in] double` a [`Float64Array`][@stdlib/array/float64] containing values to prepend after computing differences.
-   **strideP**: `[in] CBLAS_INT` stride length for `Prepend`.
-   **offsetP**: `[in] CBLAS_INT` starting index for `Prepend`.
-   **N2**: `[in] CBLAS_INT` number of indexed elements to append.
-   **Append**: `[in] double` a [`Float64Array`][@stdlib/array/float64] containing values to append after computing differences.
-   **strideA**: `[in] CBLAS_INT` stride length for `Append`.
-   **offsetA**: `[in] CBLAS_INT` starting index for `Append`.
-   **Out**: `[out] double` output [`Float64Array`][@stdlib/array/float64]. Must have `N + N1 + N2 - 1` indexed elements.
-   **strideOut**: `[in] CBLAS_INT` stride length for `Out`.
-   **offsetOut**: `[in] CBLAS_INT` starting index for `Out`.

```c
void stdlib_strided_dediff_ndarray( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, const CBLAS_INT N1, const double *Prepend, const CBLAS_INT strideP, const CBLAS_INT offsetP, const CBLAS_INT N2, const double *Append, const CBLAS_INT strideA, const CBLAS_INT offsetA, double *Out, const CBLAS_INT strideOut, const CBLAS_INT offsetOut );
```

</section>

<!-- /.usage -->

<!-- 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>

<!-- /.notes -->

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

<section class="examples">

### Examples

```c
#include "stdlib/blas/ext/base/dediff.h"
#include <stdio.h>

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

    // Define a list of values to prepend:
    const double p[] = { -1.0 };

    // Define a list of values to append:
    const double a[] = { 10.0 };

    // Define an output array:
    double out[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

    // Compute forward differences:
    stdlib_strided_dediff( 8, x, 1, 1, p, 1, 1, a, 1, out, 1 );

    // Print the result:
    for ( int i = 0; i < 9; i++ ) {
        printf( "out[ %i ] = %lf\n", i, out[ i ] );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@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> -->

<!-- </related-links> -->

</section>

<!-- /.links -->
