// the trick is to get gids spatially adjacent according to gidfunc.hoc
// in the same block. Ie gid = x + y*Nx
iterator pcitr() {local xb, yb, bx, by, x, y, k, gid
	k = 0
	xb = pc.id%(Nx/blockNx)
	yb = int(pc.id/(Nx/blockNx))
	for bx=0, blockNx-1 for by=0, blockNy-1 {
		x = bx + xb*blockNx
		y = by + yb*blockNy
		gid = loc2gid(x, y)
if (gid < 0) {
printf("%d loc2gid(%d,%d)=%d xb=%d yb=%d bx=%d by=%d\n", pc.id, x,y,gid,\
xb, yb, bx, by)
}
		$&1 = gid
		$&2 = k
		iterator_statement
		k += 1
	}
}