The field-line tracing utility for BOUT++ is written in IDL, which makes taking
advantage of a multi-core machine problematic, but not impossible.

IDL can use it's own built-in Widget objects to execute commands in parallel
on different processors. To do this however, an active X-window connection must
be maintained (i.e. leave your terminal open).

The Hopper batch script just launches one version of IDL on a compute node.
This then runs the mt_poincare.pro IDL script. Currently, this only allows one
to produce Poincare plots at different time indices simultaneously. The multi-
threading has not been included to speed up processing an individual time index.

Field-line tracing options are changed in the IDL script.

-JPS
