NAME
        LongitudeShift

   DESCRIPTION
         Performs a circular shift of a lattice along the i-direction,
        adding 360 to the x-coordinate of each wrap-around point.  For
        example, shifting a lattice with 36 i-points running 
        0,10,20,...,350 by 2 i-points will yield a new lattice with 
        x-coordinates 20,30,...,350,360,370.
        
         This module was originally developed to shift lat-lon global
        arrays along the longitude direction so that a different part 
        of the globe could be put at the center of the picture.

   INPUTS

      A1 -- Lattice
         (2-D, 1-vector, float, perimeter).
          Lattice to be shifted.

   WIDGETS

      No. I points to shift -- Slider
          The number of points by which to shift the lattice.

   OUTPUTS

      A2 -- Lattice
         (2-D, 1-vector, float, perimeter).
          "Shifted" lattice.

   KNOWN PROBLEMS
       - No check is made to see if the data looks like a good candidate for
          circular shifting;  for example, shifting a lattice with 4 i-points 
          covering 10-40 degrees longitude by 2 i-points will end up with x-coords
          of 30,40,370,380;
       - Some modules may complain that the new longitudes are > 360 degrees;
       - This module really needs some expansion:
           - 3-D lattices
           - more than one data variable (eg, winds)
           - option to add something other than 360 to shifted coordinates
           - option to do a circular shift of the x-coordinates

   SEE ALSO
       LongitudeExtend