[petsc-users] Questions about TS

[Matthew Knepley]

On Wed, Oct 19, 2011 at 3:54 PM, Blaise Bourdin <bourdin at math.lsu.edu>wrote:

> 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 section outdated?
>

Yes. What you want is to use TSSetIFunction() and TSSetIJacobian(). Jed and
Sean have added some nice examples under TS
of this, and in the latest release there is a manual section.

Let us you know if these are unclear.

  Thanks,

     Matt

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
>
>
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>


-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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