What-if algorithm

[Xho Jingleheimerschmidt]

No, it's not irrelevant. It's the key to solve the problem.
Playing with a financial function, the bisection method works,

Depending on what your "financial function" is.

but
how could I garantize that every function could be reformulated as
f()-XXX and expect the method works?

You can't, whether in Excel or Perl. And I've been exposed to plenty of
both to know. The ultimate responsibility lies with you, either way.
If you don't like it, take a demotion.

Xho

 

[gamo]

Depending on what your "financial function" is.

Put a contra-example.