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Scilab Help >> UMFPACK Interface (sparse) > taucs_chinfo

taucs_chinfo

get information on Cholesky factors

Syntax

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

• taucs_chfact — cholesky factorization of a sparse s.p.d. matrix
• taucs_chsolve — solves a linear s.p.d. system A*X = B from Cholesky factors of the sparse A
• taucs_chdel — utility function used with taucs_chfact
• taucs_chget — retrieve the Cholesky factorization at the scilab level