# taucs_chinfo

get information on Cholesky factors

## Calling Sequence

    [OK, n, cnz] = taucs_chinfo(C_ptr)

## Arguments

C_ptr

  a pointer to a Cholesky factorization

OK

  a scalar boolean

n

  a scalar integer

cnz

  a scalar integer

## Description

This function may be used to know basic information about the Cholesky factor created with taucs_chfact :

- first `OK` is `%t` if `C_ptr` is a valid pointer to an Cholesky factorization (and `%f` else)

- if `OK` is `%t` then `n` and `cnz` are respectively the matrix order and the number of non zeros elements in the supernodal structure storing `C` ; if `OK` is `%f`, `n` and `cnz` are set to the void matrix [].

## Details

Due to the supernodal structure used for `C`, `cnz` is larger than the exact number of non-zeros elements in `C` (and so this `cnz` is a mesure of the memory used internally). To get the exact `cnz` you may retrieve the Cholesky factor with taucs_chget then apply the nnz scilab function (see the 2d example in taucs_chget).

## Examples

    // Example #1 : a small linear test system
    // whom solution must be [1;2;3;4;5]
    A = sparse( [ 2 -1  0  0  0;
                 -1  2 -1  0  0;
                  0 -1  2 -1  0;
                  0  0 -1  2 -1;
                  0  0  0 -1  2] );
    b = [0 ; 0; 0; 0; 6];
    Cp = taucs_chfact(A);
    [OK, n, cnz]=taucs_chinfo(Cp)

    // Example #2 a real example
    // first load a sparse matrix
    [A] = ReadHBSparse(SCI+"/modules/umfpack/examples/bcsstk24.rsa");
    // compute the factorization
    Cp = taucs_chfact(A);
    [OK, n, cnz]=taucs_chinfo(Cp)

## See Also

- taucs_chfact
- taucs_chsolve
- taucs_chdel
- taucs_chget