Umfpack_di_numeric failed error

General Discussion
1

I am trying to solve natural convection flow inside a square cavity for a higher value of Rayleigh number (Ra=10^8), for this I took mesh = 200 but received “umfpack_di_numeric failed” error. How to deal with this problem?

2

I thick you matrix is not invertible or to big

3

Thank you Professor @frederichecht , how I can overcome this problem?

4

Debug, I try to under where is the problem.