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 Purpose: Calculates the difference between two wavefunctions
          or density operators. See review Eqs.(159-163) for a
          definition of the output.


 Usage  : overlap [-f -i -o -a -b -c -t -n -nofs -w -ig -p -ver -h -?]  [Psi] .

Options : 
 -f FILE : The wavefunction (density operator) 
           is read from file FILE rather than from ./psi.
           If FILE is a directory containing psi it must end with a /
           The string FILE may be a relative or a full path-name.
 -i FILE : Same as -f FILE.
 -o FILE : The overlaps are written to file FILE.pl rather than to ./ovl_XXX
           The string FILE may be a relative or a full path-name.
           If FILE=no, i.e. "-o no", no ovl-file will be opened.
 -nofs   : No transformation to fs. Use when "time-not-fs" was set in mctdh.
 -a      : Compute the overlaps according to their position on psi-file,
           i.e. times (tpsi) are ignored.
 -b      : Compute the overlaps ,
           i.e. the bra-state runs backwards in time.
 -c      : Compute the overlaps ,
           i.e. the complex-symmetric scalar product is used.
 -p      : Compute in addition the projections of the two sets of SPFs onto
           eachother, i.e. trace O^dagger O, where O is the SPF-overlap matrix.
 -s s s1 : Compute the overlaps < Psi(t)_s|Psi1(t)_s1>,
           s and s1 denote the electronic states of bra- and ket-WF.
 -t tend : Compute the overlap only up to t=tend.
 -n step : Compute the overlap only every step-th output.
 -w      : An existing overlap file is overwritten.
 -ig     : Ignore "different bases" error-msg.
 -ver    : Version information about the program 
 -h      : Print this help text. 
 -?      : Print this help text. 
 
 The argument Psi (bra-states) is the name of the file containing
 the comparison wavefunction or density operator.
 The ket-states are read from ./psi or from the file given by the -f option.
 If no argument is given, the user is prompted for the missing argument.
 If one calculates the overlap between density operators of different types,
 [Psi] has to be the one of type II.
 NB: The overlap is written to the file ./ovl_XXX, the screen-output
 shows the error=||Psi-Psi1||. See chapter 8.2 of the MCTDH review.
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