Re: fsolve() nasty bug ?

[Christophe Prud'homme]

Hi John

thanks for answering

| I don't see how this can happen.  
I know! that's why I sent an email asking for explanation

| In src/DLD-FUNCTIONS/fsolve.cc, the 
| following code is the only use of the nonlinear equation solving object:
|
|       NLEqn nleqn (x, nleqn_fcn);
|       nleqn.set_options (fsolve_opts);
|
|       octave_idx_type info;
|       ColumnVector soln = nleqn.solve (info);
|
|       if (fcn_name.length())
|       clear_function (fcn_name);
|       if (jac_name.length())
|       clear_function (jac_name);
|
|       if (! error_state)
|       {
|         std::string msg = nleqn.error_message ();
|
|         retval(2) = msg;
|         retval(1) = static_cast<double> (hybrd_info_to_fsolve_info (info));
|
|         retval(0) = soln;
|
|         if (! nleqn.solution_ok () && nargout < 2)
|           error ("fsolve: %s", msg.c_str ());
|       }
|
| I don't see how there could possibly be a difference among any of
|
|   x = fsolve (...);
|   [x, info] = fsolve (...);
|   [x, info, msg] = fsolve (...);

Yes I 100% agree. However testing the code with octave 2.1.73 and 2.9.5 under 
debian, shows that it matters to get fsolve converging (hence 'nasty')

|
| since the code path is exactly the same and INFO is computed and returned
| whether or not you ask for it.
|
| Also, in the code you sent, the only calls to fsolve that I see are
|
| | for the_t=tt(2:end)
| |     if ( exist('OCTAVE_VERSION') )
| |       [w, info] = fsolve("myfun",the_y);
| |     else
| |         w = fsolve('myfun',the_y,options);
| |     end
| |     u = [u w];
| |     the_y = w;
| | end
|
| so when running your code with Octave, it seems that only one case is
| tested.  Or am I missing something here?

yes the other case is for matlab (ie when OCTAVE_VERSION does not exist)

I edited the files a bit and made it clearer by removing the matlab parts.

now if I try in cranknc, 

w =fsolve(...)

and 

[w info]=fsolve() or [w info msg]=fsolve()

the first case fails, the second and third succeed

|
| If you think there is a bug, please submit a complete bug report to
| the address@hidden list with an example that clearly demonstrates the
| problem (it would help if you could eliminate the on-the-fly creation
| of a function from another function if that is not central to the bug
| report).
There is a bug (100% reproducible on different debian installations/distros at 
least) and I will fill a bug report ASAP. 

Best regards
C.
-- 
Christophe Prud'homme
EPFL SB IACS CMCS
MA B2 534 (Bâtiment MA)
Station 8
CH-1015 Lausanne
Tel: +41 (0)21 693 25 47
Fax: +41 (0)21 693 43 03

cranknic.m
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cranknic_test2.m
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