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bug#58929: 29.0.50; Calc: finding roots utpn doesn't work as advertised
From: |
Mattias Engdegård |
Subject: |
bug#58929: 29.0.50; Calc: finding roots utpn doesn't work as advertised |
Date: |
Tue, 1 Nov 2022 17:51:11 +0100 |
Unfortunately straight Newton won't converge for this function (erf,
essentially) if you stray too far from the origin (ie, the mean) so I suggest
you always use that as a starting guess no matter what point you are trying to
find the inverse for.
Another way is to use an interval as starting guess instead of a single point;
that seems to make Calc switch tactics and persevere.
One thing that can happen is running out of stack, because many of the
implementations like math-newton-root are recursive. This should be easy to
remedy as they all seem to be tail calls.
Obviously the claim to guarantee a solution for "any initial guess" is fanciful.
- bug#58929: 29.0.50; Calc: finding roots utpn doesn't work as advertised,
Mattias Engdegård <=