*You can set here the solver type to one of diagonal,
matrix_iterative_bicg, matrix_iterative_petsc or matrix_superlu.
The solver set here holds for the entire calculation (as opposed
to the control_options_solver which only holds for the corresponding time steps).
In fact, each control_options_solver will be overwritten by a specified options_solver.
*

*You can also set an environment symbol
TOCHNOG_OPTIONS_SOLVER to solver, by example to -matrix_superlu.
In this way, you do not need to set the solver type in each input file separately.
*

tochnog 2001-09-02