semi coarsening with DA's

[Dave May]

Hello,
    Does anyone know the best way to perform semi coarsening using DA's?
I was trying to use the following grid sequence
  level [2]: 20 x 20
  level [1]: 11 x 11
  level [0]: 6 x 6
where the numbers M x N corresponds to the number of nodes in the x and y
direction respectively.
However I was unable to generate the interpolation operator using
  DAGetInterpolation(DA dac,DA daf,Mat *A,Vec *scale)
Doing so caused the following error
  [0]PETSC ERROR: Arguments are incompatible!
  [0]PETSC ERROR: Ratio between levels: (mx - 1)/(Mx - 1) must be integer:
mx 20 Mx 11!

Is there a more general way to construct the interpolation operator
within petsc for this type of grid sequence?

Thanks,
  Dave.
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