Purpose: Generates 2D-densities from the wavefunction.
 Usage:   dengen [-i -f -n -skip -step -o -rst -pop2 -nw -w -ver -h -?] f1 f2

Options : 
 -i DIR  : data is stored in directory DIR
 -f FILE : the wavefunction is read from FILE rather than from ./pes
           The string FILE may be a relative or a full path-name.
 -o FILE : The ouput is written to file FILE rather than to ./dens2d.dat
           The string FILE may be a relative or a full path-name.
 -n num  : only num WFs are processed.
 -skip m : the first m WFs are skipped.
 -step step : only every step's WF will be processed.
 -rst    : the restart file is read,  rather than the psi file.
 -nw     : No weights are employed. Plot the "naked" DVR populations.
 -pop2   : the basis set occupations are plotted rather than grid
           populations. For FFT this implies momentum space representation.
 -w      : Overwrite the output file.
 -ver    : Version information about the program.
 -h      : Print this help text. 
 -?      : Print this help text. 

  The arguments f1 and f2 denote the DOFs for which a 2D-density is generated.
  The arguments f1 and f2 may be integers or modelabels.

  If there are more WFs on psi file than you want to inspect, use the
  options -n, -skip, or -step. Example: "dengen -skip 10 -n 2 rd rv" will
  generate densities of the WFs no. 11 and 12 (i.e. t=10 and 11 if tpsi=1fs),
  and "dengen -step 10 -n 2 rd rv" will gen. dens. of the WFs no. 1 and 11.
  NB: The option -pop2 is ignored for phifbr,sphfbr,k,external bases.
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