I have, say, an ellipse in the x-y plane: (x^2/a^2) + (y^2/b^2) = 1 I want a 3d (e.g. z) function where inside the ellipse z=+1, outside z=0; the function is not continuous. so in effect what I'm left with is a large plane where z= 0, and a small ellipse cut out raised to z=1. How do I write what I want in terms that i can implement it in computations. %this problem comes from describing quantum dots in 2 and 3 dimensions.