[Octave-bug-tracker] [bug #54952] optimset (old, new) uses empty fields from 'new'

[Kai Torben Ohlhus]

Update of bug #54952 (project octave):

                  Status:                   Fixed => None                   
             Open/Closed:                  Closed => Open                   

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Follow-up Comment #3:

Sorry for opening this one again, but it triggered bug #55089.

The reason is a strange recursive interplay by
"scripts/optimization/__all_options__" and "scripts/optimization/optimset". 
It took me some time to understand it to 95% yet.

__all_options__ contains a persistent variable "save_names" [1] that gets
filled by calling a Matlab compatible feature of "optimset" [2,3], but [2]
does not make it very obvious that a call like


optimset ('fsolve')


is fully legitimate.  This call invokes


fsolve ('defaults')


which in turn calls "optimset" with, guess what, EMPTY VALUES! [4]  Pure
horror ^^

So my solution out of this misery was to change all instances in
"scripts/optimization" like [4] to return pure structs.  I think the recursive
output validation by optimset is not necessary and I support the changes made
so far with the non-emptiness check, which is also R2018b compatible.

This way both calls return the correct values:


>> optimset ('fsolve')
>> fsolve ('defaults')
ans =

  scalar structure containing the fields:

    AutoScaling = off
    ComplexEqn = off
    FunValCheck = off
    FinDiffType = forward
    Jacobian = off
    MaxFunEvals = [](0x0)
    MaxIter =  400
    OutputFcn = [](0x0)
    Updating = off
    TolFun =  0.0000010000
    TolX =  0.0000010000
    TypicalX = [](0x0)



The only thing I did not find out yet was, when does this persistent variable
gets filled?  Because at every start of Octave it contains the right values?!

[1]
https://hg.savannah.gnu.org/hgweb/octave/file/c197655f9d28/scripts/optimization/__all_opts__.m#l29

[2]
https://hg.savannah.gnu.org/hgweb/octave/file/c197655f9d28/scripts/optimization/optimset.m#l31

[3]
https://hg.savannah.gnu.org/hgweb/octave/file/c197655f9d28/scripts/optimization/optimset.m#l133

[4]
https://hg.savannah.gnu.org/hgweb/octave/file/c197655f9d28/scripts/optimization/fsolve.m#l175

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