Fix#4167. That problem was initially reported as a problem with TINV, however, at its root, it was actually a problem with TDIST (which TINV needs to call). Both of these are deprecated by Microsoft in favor of some newer functions. PhpSpreadsheet incorrectly treated T.INV as an alias for TINV, and did not implement T.INV.2T, which actually is an alias for TINV.
To solve this problem, I adapted the Perl CPAN module `Statistics::Disttributions`, written by Michael Kospach around 2003. Unit test results have been manually checked against Excel; a few had to be changed because they were wrong (see the original issue). I believe that all of TDIST, T.DIST.2T, T.DIST.RT, TINV, T.INV, and T.INV.2T now function correctly, at least most of the time. I have not found code or an algorithm that I can use for T.DIST nor for T.TEST, both of which remain unimplemented.
While we might never be able to have 100% of our code strict, we can at
the very least do it for all of our tests. This ensures that our tests
are using our API with the types as intended by the test author, and not
silently be cast to what our API requires.
* Start implementing Newton-Raphson for the inverse of Statistical Distributions, starting with the two-tailed Student-T
* Additional unit tests and validations
* Use the new Newton Raphson class for calculating the Inverse of ChiSquared
* Extract Weibull distribution, and provide unit tests
oleibman
Adrien Crivelli
Mark Baker