[Octave-bug-tracker] [bug #53991] Octave crashes using fsolve when x0 is a stationary point

[Marco Caliari]

Follow-up Comment #6, bug #53991 (project octave):

@Rik: my first thought was that info = -2 should be set when fjac is small AND
fvec is still large. So I tried


[~, ~, flag] = fsolve (detB, pi)


(pi is the right solution), but I get flag = -3. I would conclude that:

1) fsolve should check whether the initial solution is already fine before the
## Outer loop

2) when it computes a new fjac, it means that the previous fvec was not fine.
Therefore it is correct just to check whether the new fjac is not too small,
as you did

3) I would use norm (fjac, 1). The 1-norm is easier to compute.

4) For unconverged cases, Matlab gives a message (not a warning).

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