  mesh
    rectilinear
      nx = 10
      ny = 10
      bx =  3
      by =  3
      gmin = -1.0 -1.0
      gmax =  1.0  1.0
    end
    user defined geometry transformation
     "
     double r = sqrt(inxcoord*inxcoord+inycoord*inycoord);
     double theta = atan2(inycoord,inxcoord);
     if(r > 0.5)
      {
        theta = theta + (3.14159 / 4.0)*((r-0.5)/0.5);
        outxcoord = r*cos(theta);
        outycoord = r*sin(theta);
      }
     "
    end
  end
