I wanted to get opinions on whether solving this problem in a non-numerical way is realistic, or if someone has the answer, all the better. I have a totally arbitrary ellipsoid (not aligned with any axes) that I can describe by matrix A, like x'Ax=1 is the ellipsoid surface. I have the points describing the primary axes of the ellipse. What I want is to cut the ellipse by a plane at Z=(some value) and get the volume above/below that plane. One approach that seems potentially doable is to solve for the area of the ellipse generated by a cut at Z=x and then integrate that over the range of interest. How exactly to carry that out is eluding me at the moment though. Thanks for any input.