Re: solving triadiagonal (and banded in general) systems of linear equations

[Jordi Gutiérrez Hermoso]

On 26 September 2012 18:48, Sergei Steshenko <address@hidden> wrote:

> So, do I understand it correctly, that I simply need to provide
> matrix to the solver, and it will detect automatically that the
> matrix is banded and choose the most optimal algorithm ?

    
http://hg.savannah.gnu.org/hgweb/octave/file/46dd555edd33/liboctave/array/MatrixType.cc#l268

Note that the argument for this function is a sparse matrix, so the
check only occurs for sparse matrices. For full matrices the check is

     
http://hg.savannah.gnu.org/hgweb/octave/file/46dd555edd33/liboctave/array/MatrixType.cc#l60

only upper, lower, and hermitian matrices. No bandedness is checked if
the matrix isn't of sparse type. This is consistent with the
documentation:

    octave:1> x = toeplitz ([1 2 0 0 0 0]); y = toeplitz ([1 2 3 0 0 0]);
    octave:2> matrix_type (x), matrix_type (y)
    ans = Full
    ans = Full
    octave:3> matrix_type (sparse (x)), matrix_type (sparse (y))
    ans = Tridiagonal
    ans = Banded

HTH,
- Jordi G. H.