 that <a href="vshift.html">VSHIFT</a> is similar to Matlab's CIRCSHIFT, but has the opposite
    convection for positive and negative shifts. 
 
    ------------------------------------------------------------------
    Y=<a href="vshift.html">VSHIFT</a>(X,N,DIM,INDEX,DIM2) applies this shift selectively, only to
    that subset of X obtained by indexing X with INDEX along DIM2, i.e.
 
 		    1 2      DIM2     DIMS(X)
 		    | |        |         |
 		  X(:,:, ... INDEX, ..., :)	
 
    is cycled N places al