umf_luinfo

get information on LU factors

Calling Sequence

[OK, nrow, ncol, lnz, unz, udiag_nz, it] = umf_luinfo(LU_ptr)

Arguments

:LU_ptr a pointer to umf lu factors (L,U,p,q, R) : :OK a scalar boolean : :nrow, ncol, lnz, unz, udiag_nz, it scalars (integers) :

Description

This function may be used to know basic information about LU factors created with umf_lufact :

first OK is %t if LU_ptr is a valid pointer to an umfpack LU numeric handle (and %f else)

if OK is %t then:

:nrow, ncol are the matrix size (L is nrow x n and U is n x ncol

where n = min(nrow,ncol)

: :lnz, unz are the number of non zeros elements in L and in U; : :udiag_nz are the number of non zeros elements on the diagonal of U;

if the matrix is square ( nrow = ncol = n) then it is not inversible if udiag_nz < n (more precisely it appears to be numericaly not inversible through the LU factorization).

: :it 0 if the factors are real and 1 if they are complex. :

if OK is %f then all the others outputs are set to the empty matrix [].

Examples

// this is the test matrix from UMFPACK
A = `sparse`_( [ 2  3  0  0  0;
              3  0  4  0  6;
              0 -1 -3  2  0;
              0  0  1  0  0;
              0  4  2  0  1] );
Lup = `umf_lufact`_(A);
[OK, nrow, ncol, lnz, unz, udiag_nz, it] = umf_luinfo(Lup)  // OK must be %t, nrow=ncol = 5,
[L,U,p,q,R] = `umf_luget`_(Lup);
`nnz`_(L)  // must be equal to lnz
`nnz`_(U)  // must be equal to unz
`umf_ludel`_(Lup) // clear memory

See Also

• umfpack solve sparse linear system
• umf_lufact lu factorisation of a sparse matrix
• umf_lusolve solve a linear sparse system given the LU factors
• umf_ludel utility function used with umf_lufact
• umf_luget retrieve lu factors at the scilab level