toCompact

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

Installation

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

Usage

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.

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.

Examples

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 ]
    ]
*/

Notice

This package is part of 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, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.