Polyharmonic splines on grids IMG WIDTH=''78'' HEIGHT=''38'' ALIGN=''MIDDLE''BORDER='' ''SRC=''http://www.ams.org/mcom/2005-74-252/S0025-5718-05-01753-9/gif- -title0/img1.gif'' ALT=''\mathbb{Z}\times a\mathbb{Z} {n}''> and their limits