[petsc-users] (Fast?) assembly of upper triangle and MatZeroRows

[Clemens Domanig]

Hi,

I want my FE-program to be able to use LU- and LDLt-decomp (MUMPS). LU 
works fine and now I want to implement LDLt. My Questions:
1.) How can I speed up the assembly of the upper triangle matrix?
* '-mat_ignore_lower_triangular' makes it terrible slow
(1000 elements -> 1s explode to 18s
* MatSetValues with Blocks of 6x6 and single values at the diagonal is 
even worse.
2.) SBAIJ doesn't like MatZeroRows. What are the alternatives to apply 
boundary conditions to my matrix?


Thx for your help - Clemens