Libmesh Time-Dependent Problems

In version 0.5.0, you must reassemble your entire matrix and right-hand side at each time step. I do not need to speak of the inefficiency of this. The developer's speak of a the option of not doing this at each time step but I do not see how that is other than rewriting the code. Look on line 153 of 'implicit_system.C' for the assemble routine that zeros out the matrices and rhs's creating the need for reassembly.

The option 'System::assemble_before_solve' has been added in CVS to the "System class":http://libmesh.sourceforge.net/doxygen/classSystem.php. 'include/solvers/system.h' revision 1.18 has:

date: 2006/02/16 22:17:57;  author: jwpeterson;  state: Exp;  lines: +21 -1
Added a boolean flag to the system class which allows you
to skip assembling during the solve step if you know that for some reason the
system has already been assembled e.g. during a previous call to assemble().
This can be useful if you are solving an implicit system with multiple right
hand sides where you will need to solve multiple times but only assemble once.

Use of the option is mentioned in the mailing lists: "Controlling when to assemble":http://sourceforge.net/mailarchive/message.php?msg_id=17137234.