SteadyState

use columns and not only rho and v.

for example given a file with the format:
fr rho v j

one may give:
-c 0 1 2 3
-rs 60 100 300
-re 100 150 400

which means:
- use columns 0, 1, 2, and 3
  - columns 1 from 60 to 100
  - columns 2 from 100 to 150
  - columns 3 from 300 to 400

- xlabel: time or frame
- better file names (no *.txt.txt or *.txt.png)