Re: passing a structure to fsolve

[Olaf Till]

On Tue, Mar 22, 2011 at 01:03:59PM -0700, altomare wrote:
> Hi all,
> 
> I would like to pass a structure to fsolve but so far I did not have any
> luck
> Minimal example:
> %%
> clear all
> 
> function r = gtest(str)
> r=str.a-str.b;
> endfunction
> test.a=2;
> test.b=3;
> 
> 
> If I type: gtest(test) I get 
> ans = -1
> However 
> [x, fval, info] = fsolve (@(var) gtest(var),test)
> returns:
> error: Invalid call to fsolve.  Correct usage is: ...
> It looks to me that I cannot pass a structure to fsolve.

Yes, you can only pass a vector or matrix.

> If that is the
> case, how can I circumvent the problem?

Well, you have to pass all initial values as elements of a single
vector or matrix. fsolve will call your function (anonymous function @
(var) in your example) with a vector (or matrix, respectively)
argument. You could try to reorder the vector (or matrix) elements to
provide a structure for the call to "gtest":

... = fsolve (@ (var) gtest (<some functions> (var)), init_vals);

where <some functions> might involve "reshape", "num2cell",
"cell2struct", or even "partarray" from the miscelaneous package
(Octave Forge). Or you could put <some functions> into the body of
gtest instead. Or it might be easier to make getest directly use the
vector (or matrix).

Olaf