Long Run Time on Lecture causing build cache issues

[mmcky]

@kp992 this lecture

https://python-advanced.quantecon.org/black_litterman.html

is taking a very long time to run.

I suspect this is worse than in the past.

Would you have time to review this lecture to see if we can compute it under 3000minutes?

[kp992]

Thanks for pointing that out @mmcky. I can have a look at it and try to optimize it.