Wrong results in calculation

I have quite a few algorithms I programmed which behave as I claim. I showed in the forum
when I was learning Julia last year two toy examples:

-Computing the inverse of a Hilbert matrix:
Julia slow with Hilbert matrices

-Computing the collatz function:
A plea for int overflow checking as the default - #46 by Olof_Salberger

I have many serious programs behaving the same way, but they are a bit too technical to give in this forum