[nfc][hist] clarify bigaus argument order

[ferdymercury]

No description provided.

[guitargeek]

Why was the list in the line just before in the docs not sorted consistently? That's a bit surprising. But well, this new line definitely clarifies things.

[ferdymercury]

Why was the list in the line just before in the docs not sorted consistently? That's a bit surprising.

Not sure what you mean?
bigaus is defined with an order of parameters that differs from ROOT::Math::bigaussian_pdf(...) function
So the docs were right, just missing more detail?

[guitargeek]

I mean that I didn't like that the ordering of the parameters passed to the bigaus substitute in TFormula is not consistent with the parameter order of ROOT::Math::bigaussian_pdf, which became obvious from the documentation. We should be more consistent with these things inside ROOT in my opinion.

Of course that's nothing we can change at this point, so it was just a random rant. Sorry 🙂

[ferdymercury]

I mean that I didn't like that the ordering of the parameters passed to the bigaus substitute in TFormula is not consistent with the parameter order of ROOT::Math::bigaussian_pdf, which became obvious from the documentation. We should be more consistent with these things inside ROOT in my opinion.

Of course that's nothing we can change at this point, so it was just a random rant. Sorry 🙂

Ahhh yeah, I got you now. Yeah, too late to change.

Maybe the problem was that originally bigaus was an extension of gaus or xygaus so it started from that order
whereas Math::bigaussian was supposed to be centered at zero and later evolved to have also an offset as last parameters.
But @couet might remember the details better.

Btw related: https://root-forum.cern.ch/t/whats-the-predefined-function-bigauss/45572