Thanks a lot! I missed that part. I cleaned the code and updated the question. I have modified my code so that the sampling is non-centered distribution, I read that it can speed up the sampling. That improved the sampling rate but even with that if I am trying to scale it to n = 100 or n = 10 in this case, the sampling is extremely slow. It takes more than 3 seconds to get a sample. Am I still missing something here?