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Purpose   : Reads the lownatpop file and prints the maximum over time
            of the populations for all listed nodes and modes.
            The four highest and four lowest populations will be marked.

Usage     : lownp.py [-h, -f, -t, -last, -min, -max]
Options   :  -h  Print this help-text (--help and -? also work).
             -f       "path" is the path to the file to be analyzed.
                            If the -f option is not given,
                            path=./lownatpop is assumed.
             -tmin      Analyze only data with time >= ti.
             -tmax      Analyze only data with time <= tx.
             -last          Analyze only data of the last time point.
             -min   Mark all populations which
                            are < mimpop with '+'.
             -max   Mark all populations which
                            are > maxpop with '*'.
             -skip          Skip the first two lines.
                            This is useful when electronic states are present.

Examples  : lownp.py -f ../run2/lownatpop
            lownp.py -max 1.e-4 | grep '*'

This script has been tested with Python version 2.7.16
HDM 02/20
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