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 Purpose: Calculates the difference between two A-vectors.
          See review Eqs.(159-163) for a definition of the output

 Usage  : aoverlap83 [-f -i -o -n -w -ver -h -?]  [psi2] .

Options : 
 -f FILE : The wavefunction is read from file FILE rather than from ./psi
           The string FILE may be a relative or a full path-name.
 -i FILE : Same as -f FILE.
 -o FILE : The difference is written to file FILE.pl rather than to ./aovl_XXX
           The string FILE may be a relative or a full path-name.
           If FILE=no, i.e. "-o no", no aovl-file will be opened.
 -abs    : Take the absolute value of A, when computing the overlap.
 -n step : Compute the A-overlap only every step-th output.
 -w      : An existing aoverlap file is overwritten.
 -ver    : Version information about the program 
 -h      : Print this help text. 
 -?      : Print this help text. 
 The argument psi2 is the name of the file containing the comparison
 wavefunction.
 If no argument is given, the user is prompted for the missing argument.
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