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See the recommended documentation of this function

Scilab help >> UMFPACK Interface (sparse) > taucs_chinfo

# 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
// compute the factorisation
Cp = taucs_chfact(A);
[OK, n, cnz]=taucs_chinfo(Cp)```

• taucs_chfact — cholesky factorisation of a sparse s.p.d. matrix
• taucs_chsolve — solve a linear sparse (s.p.d.) system given the Cholesky factors
• taucs_chdel — utility function used with taucs_chfact
• taucs_chget — retrieve the Cholesky factorization at the scilab level