Numerical Instability Problem Solved with CPU-version C++ .find_span() for curve_eval.cpp

[mechyai]

I was dealing with frequent 'randomly' occurring Nan results for the basis function evaluations when using the CPU, C++ curve_eval.cpp -- curve_pre_compute_basis(...) function which is used in curve_eval.py here (just for those new to this repo and facing the same issue). This would would then cause Nan in the curve evaluation and destroy any torch optimization loop.
I was able to solve this issue by removing the eps values in the .find_span() function here:

NURBSDiff/NURBSDiff/csrc/utils.cpp

Line 20 in 1493c16

while (u < U[mid]-eps || u >= U[mid+1]+eps){