npm package: @stdlib/array-base-symmetric-banded-to-compact
Description: Convert a two-dimensional symmetric banded nested array to compact banded storage.
Author: The Stdlib Authors
Latest version: 0.1.1

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# toCompact

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> Convert a two-dimensional symmetric banded nested array to compact banded storage.

<!-- 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>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-symmetric-banded-to-compact
```

</section>

<section class="usage">

## Usage

```javascript
var toCompact = require( '@stdlib/array-base-symmetric-banded-to-compact' );
```

#### toCompact( uplo, arr, k, colexicographic )

Converts a two-dimensional symmetric banded nested array to compact banded storage.

```javascript
var x = [ [ -1, 2, 0 ], [ 2, -2, 4 ], [ 0, 4, -3 ] ];

var out = toCompact( 'upper', x, 1, false );
// returns [ [ 0, 2, 4 ], [ -1, -2, -3 ] ]
```

The function accepts the following arguments:

-   **uplo**: specifies whether to reference the upper or lower triangular part of the input array.
-   **arr**: input two-dimensional nested array.
-   **k**: number of super-/sub-diagonals.
-   **colexicographic**: boolean specifying whether to store diagonals in colexicographic access order.

</section>

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</section>

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<section class="examples">

## Examples

<!-- eslint-disable no-multi-spaces -->

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

```javascript
var toCompact = require( '@stdlib/array-base-symmetric-banded-to-compact' );

// Define a symmetric banded matrix:
var A = [
    [  1,  2,  3,  0,  0 ],
    [  2,  4,  5,  6,  0 ],
    [  3,  5,  7,  8,  9 ],
    [  0,  6,  8, 10, 11 ],
    [  0,  0,  9, 11, 12 ]
];

// Convert the upper triangle to lexicographic compact form:
var AC = toCompact( 'upper', A, 2, false );
/* e.g., returns =>
    [
        [  0,  0,  3,  6,  9 ],
        [  0,  2,  5,  8, 11 ],
        [  1,  4,  7, 10, 12 ]
    ]
*/

// Convert the lower triangle to lexicographic compact form:
AC = toCompact( 'lower', A, 2, false );
/* e.g., returns =>
    [
        [  1,  4,  7, 10, 12 ],
        [  2,  5,  8, 11,  0 ],
        [  3,  6,  9,  0,  0 ]
    ]
*/

// Convert the upper triangle to colexicographic compact form:
AC = toCompact( 'upper', A, 2, true );
/* e.g., returns =>
    [
        [  1,  2,  3 ],
        [  4,  5,  6 ],
        [  7,  8,  9 ],
        [ 10, 11,  0 ],
        [ 12,  0,  0 ]
    ]
*/

// Convert the lower triangle to colexicographic compact form:
AC = toCompact( 'lower', A, 2, true );
/* e.g., returns =>
    [
        [  0,  0,  1 ],
        [  0,  2,  4 ],
        [  3,  5,  7 ],
        [  6,  8, 10 ],
        [  9, 11, 12 ]
    ]
*/
```

</section>

<!-- /.examples -->

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* * *

## 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 &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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