Thank you for the reply sir.
But, when I am running both the scripts (rayleigh_benard.py and plot_snapshots.py) serially , I face the error,
DocoptLanguageError: "usage:" (case-insensitive) not found.
and when i am running only the plot_snapshots.py script , the error is,
DocoptExit: Usage:
plot_snapshots.py <files>... [--output=<dir>]
plz, help me out.