 Usage:  {g, gind} = groupcol (col, ncol)  
 
 Input:

  col                    scalar or color vector 
                         
  ncol                   scalar expected length of colorvector 
                         
 Output:

  gcol                   m x 1 different colors 
                         
  gind                   n x 1 index of groups 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
