@helloworld922 there can be other singularities but for now, just at x=0. I define $|x|=(\sum_{i=1}^{d} x_{i}^{2})^{1/2}$ and $\gamma > 0$ (generally, $f$ would contain a singularity which is counteracted somewhat by $|x|^\gamma$)

Thanks, this helped. When I was implementing for triangle elements, I hadn't even really thought about it and just computed the inverse mapping since it was easy. I'm adapting my code to quad elements now and fell into following the same formula that was already implemented, completely overlooking the easiest way to do this facepalm Thanks again