Incomplete fractorisation (IF) preconditioning for conjugate gradient method!!!

hello,
I'm Trying to run a unsaturated transient flow,
When running the simulation, at each step, it was marqued at the bottom of the Feflow window these messages:
- assembling matrix for the flow equations
-computing discontinuous velocity field
-drawing fringed fiels

and [b]-Incomplete fractorisation (IF) preconditioning for conjugate gradient method

What does this message mean??

Thank you very much!

Hi Sana,

this log message indicates that the matrix which has to be solved is nonsymmetric. Thus not the standard PCG solver is used, but a nonsymmetric one, default is the Preconditioned Lanczos BiCGSTABP. Preconditioning the matrix is done in order to speed up the solution process.

Dear Bastian,

If the equation system is nonsymetric and using  the Precoditioned lanczos type BiCGSTABP method (default), Why I have the log message with IF PCG  :o

In my cense,  PCG IF is specific to symmetric equations systems)!!!!

Thanks!

Dear Sana,

the IF preconditioning is not specific for symmetric systems. As stated here:

[url=http://www.feflow.info/html/help/HTMLDocuments/reference/dialogs/problemsettings/solver_type.htm]http://www.feflow.info/html/help/HTMLDocuments/reference/dialogs/problemsettings/solver_type.htm[/url]

"All methods for solving the nonsymmetric equation systems (transport simulation) except SAMG apply the incomplete factorization (IF) preconditioning."