text: try: range = xrange
  except: pass
  
  import sys, slepc4py
  slepc4py.init(sys.argv)
  
  from petsc4py import PETSc
  from slepc4py import SLEPc
  
  Print = PETSc.Sys.Print
  
  def construct_operator(m, n):
      """
      Standard symmetric eigenproblem corresponding to the
      Laplacian operator in 2 dimensions.
      """
      # Create matrix for 2D Laplacian operator
      A = PETSc.Mat().create()
      A.setSizes([m*n, m*n])
      A.setFromOptions( )
      A.setUp()
      # Fill matrix
      hx = 1.0/(m-1) # x grid spacing
      hy = 1.0/(n-1) # y grid spacing
      diagv = 2.0*hy/hx + 2.0*hx/hy
      offdx = -1.0*hy/hx
      offdy = -1.0*hx/hy
      Istart, Iend = A.getOwnershipRange()
      for I in range(Istart, Iend) :
          A[I,I] = diagv
          i = I//n    # map row number to
          j = I - i*n # grid coordinates
          if i> 0  : J = I-n; A[I,J] = offdx
          if i< m-1: J = I+n; A[I,J] = offdx
          if j> 0  : J = I-1; A[I,J] = offdy
          if j< n-1: J = I+1; A[I,J] = offdy
      A.assemble()
      return A
  
  def main():
      opts = PETSc.Options()
      n = opts.getInt('n', 32)
      m = opts.getInt('m', 32)
      Print("2-D Laplacian Eigenproblem solved with contour integral, "
            "N=%d (%dx%d grid)\n" % (m*n, m, n))
      A = construct_operator(m,n)
  
      # Solver object
      E = SLEPc.EPS().create()
      E.setOperators(A)
      E.setProblemType(SLEPc.EPS.ProblemType.HEP)
      E.setType(SLEPc.EPS.Type.CISS)
  
      # Define region of interest
      R = E.getRG()
      R.setType(SLEPc.RG.Type.ELLIPSE)
      R.setEllipseParameters(0.0,0.2,0.1)
      E.setFromOptions()
  
      # Compute solution
      E.solve()
  
      # Print solution
      vw = PETSc.Viewer.STDOUT()
      vw.pushFormat(PETSc.Viewer.Format.ASCII_INFO_DETAIL)
      E.errorView(viewer=vw)
      vw.popFormat()
  
  if __name__ == '__main__':
      main()
  