[R] trmat, or prmat in "spatial" package

[Yan Yu]

Hello, there,
   when i tried with trmat, or prmat (the interpolation/kriging function)
in "spatial package", i found it it only did interpolation for n x n grid.
however, my data is distributed in a rectangle field, not in square, so I
would like to set different size for x and y dimension.. HOw can I set it
to be m x n grid ( m != n)?
ANy hint on how to get around this is appreciated:)
yan