Re: Passing parameters to fsolve function - new syntax?

[Michael Kopp]

Hello,

> I have a function f(x,a,b,c), which I would like solve for variable x, 
> so that f(x,a,b,c)=0, where a,b,c are parameters, which are known at the 
> time of solving.
>
> However, current fsolve function in Octave only supports one-variable 
> functions. I suppose there is a work-around to declare specific global 
> variables and then giving values to those variables before calling the 
> fsolve function, but this doesn't seem to be a clean way of organizing 
> this.
>
> The fsolve FIX in the octave-forge package seems to expand this 
> functionality, but I'm not able to compile it. Also, the status of this 
> FIX seems to be unclear, as in the development mailing list message 
> http://sourceforge.net/mailarchive/message.php?msg_id=11922522:
>
> Paul Kienzle, in May, 2005:
>
> > I have no interest in maintaining this function.  I am removing it from
> > the build system for now, and will purge it completely if nobody steps
> > forward to update it.
> >
> > IIRC, the purpose of this function is to pass extra arguments to
> > fsolve, but we can do this now with the new syntax:
> >
> >     @(x) f(x,a,b,c)
> >
> > - Paul

I was having the same problem. Actually, the message by Paul Kienzle was in
response to a question I posted on this mailing list last May. Below, I
attach my original message, which shows how I was able to compile fsolve.cc
by outcommenting some of the code. Probably, this destroys the possibility
of passing options to the function, but for my current purposes, it works fine.

I have also found another ugly work-around for the standard fsolve, using
sprintf. It goes like this:

function y = f(x,a)
    y = 2*x + a;
endfunction

a = 2;
str=sprintf('function y = g(x); y = f(x,%g); endfunction',a);
eval(str);
fsolve('g',1)

Now, here is my message from 10 May 2005:

------------------------------------------------------------------------

I was just trying to compile fsolve.cc from octave_forge/FIXES
(a link to the file can be found here:
http://octave.sourceforge.net/index/optimization.html#Rootfinding).

I used the command "mkoctfile fsolve.cc" on a PC with Suse Linux 9.1. My
version of gcc is 3.3.3.

I got the following error message:

**********************************************************************
fsolve.cc:260: error: cannot convert `double (NLEqn_options::*)() const' to
`double (NLEqn_options::*)()' in initialization
**********************************************************************

The relevant code from fsolve.cc seems to be

**********************************************************************
struct NLEQN_OPTIONS
{
  const char *keyword;
  const char *kw_tok[MAX_TOKENS + 1];
  int min_len[MAX_TOKENS + 1];
  int min_toks_to_match;
  d_set_opt_mf d_set_fcn;
  d_get_opt_mf d_get_fcn;
};

static NLEQN_OPTIONS fsolve_option_table [] =
{
  { "tolerance",
    { "tolerance", 0, },
    { 1, 0, }, 1,
    &NLEqn_options::set_tolerance,
    &NLEqn_options::tolerance, },   // here is the problem

  { 0,
    { 0, 0, },
    { 0, 0, }, 0,
    0, 0, },
};
**********************************************************************

The problem is in the line &NLEqn_options::tolerance. If I outcomment this,
the rest compiles fine. From
http://pareto.uab.es/mcreel/OctaveClassReference/html/index.html
I get the following information:

**********************************************************************
NLEqn_options Class Reference
Public Member Functions
     NLEqn_options (void)
     NLEqn_options (const NLEqn_options &opt)
NLEqn_options &     operator= (const NLEqn_options &opt)
     ~NLEqn_options (void)
void     init (void)
void     copy (const NLEqn_options &opt)
void     set_options (const NLEqn_options &opt)
void     set_default_options (void)
void     set_tolerance (double val)
double     tolerance (void) const
**********************************************************************

So the tolerance function is indeed declared with const. Unfortunately, my
rudimentary knowledge of C++ does not allow me to find a workaround other
than outcommenting the entire line. Does anyone have a better solution?

------------------------------------------------------------------------

Hope this helps,

Michael.



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