90 year data simulation in need of performance increase
This cleanup code at the end is indicative of the problem with this program:


clear i
clear j
clear k
clear l
clear m
clear n
clear o
clear p



Nobody is going to reverse-engineer your minified / obfuscated code to understand it.  You will probably have a hard time understanding it yourself if you come back to it after a few weeks.  The program is therefore unmaintainable.

I wouldn't have much confidence in the correctness of the results, either.  The code should be broken down into functions, each of which has a single purpose, specific inputs and outputs, and is separately testable.