Parameters in this block are accessed by the problem-generator,
and therefore depend on the problem being run. For example, the
problem-generator `athena1.0/src/prob/shkset.c`
(which is used for the Brio & Wu test problem)
requires the following parameter values in the `<problem>` block:

**gamma:**ratio of specific heats used in equation of state***l:**values of variable * in left-state***r:**values of variable * in right-state

2003-03-05