What language should you use for complex calculations when the logic interacts haeavily with database data?

When performing intense calculations, an obvious language choice is C or C++. However, PL/SQL is a natural choice for logic that interacts heavily with database data. If all you need to do is add or multiply a few large numbers, there's no reason you can't leverage the appropriate algorithms to perform the arithmetic in PL/SQL and still get good performance.

Another alternative to consider is Java stored procedures, which let you use extensive libraries for doing math while also having the advantage of running on the database.