# [petsc-users] Questions about TS

Blaise Bourdin bourdin at math.lsu.edu
Wed Oct 19 10:54:13 CDT 2011

```Hi,

I am trying to use TS to solve a simple transient problem in an unstructured finite element f90 code.

1. Section 6.1.1 of the manual refers to a TSSetMatrices function that can be used to set the RHS and LHS matrices, but I can;t find it. Is this section outdated?
2. Since we are using unstructured finite elements, the LHS matrix is not the identity. As far as I understand, we have two possible choices:
- Use a mass lumping approximation of the variational identity matrix (mass matrix), M, and use M^{-1}K for the RHS matrix instead of K.
- Use an IMEX method where the implicit matrix is the variational identity M.
Is this right? What is the recommended way?
3. Is src/ts/examples/tests/ex1f.F supposed to work? Is there a fortran or fortran90 example I could start from? I get the following:
galerkin:tests bourdin\$ ./ex1f -linear_constant_matrix
1  Procs Avg. error 2 norm                        NaN                       NaN  euler
galerkin:tests bourdin\$ ./ex1f
1  Procs Avg. error 2 norm                        NaN                       NaN  euler

Thanks,

Blaise

--
Department of Mathematics and Center for Computation & Technology
Louisiana State University, Baton Rouge, LA 70803, USA
Tel. +1 (225) 578 1612, Fax  +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin

```