taucs_chinfo

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 factorisation
Cp = taucs_chfact(A);
[OK, n, cnz]=taucs_chinfo(Cp)

See Also

• 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