fzero function, additional output needed

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Hi, I use fzero to find the zero of my function. fezero returns [x, fval]. however, inside the function another parameter is being calculated. I need to return that parameter back to the script that fzero comes from. how can I do that? apparently fzero doesnet return anything but x and fval!
objective function:
function [F]=find_pw(p,pw)
global qglim gamma pdew p1
if pw>= pdew
p1=pdew;
else
F=find_p11(p,pdew,pw);
if F>0
p1=pdew;
else
objectivefunction=@(p1)find_p11(p,p1,pw);
% options = optimset('Tolx',pwlim);
p1=fzero(objectivefunction,[pw,min(p,pdew)]);%,options);
end
end
mpt=mp2(p,pw,p1);
qg=gamma*mpt;
F=qg-qglim;
end
scpirt:
% ....
objectivefunctionpw=@(pw)find_pw(p,pw);
pw=fzero(objectivefunctionpw,[pwlim,pw]);%,options);
% I Need "p1" here
%...
I need the function "find_pw", to return "p1" too. thanks.

Accepted Answer

José-Luis
José-Luis on 2 May 2013
Is there anything preventing you from modifying find_pw() to return p1 as well?
function [F,p1]=find_pw(p,pw)
Globals are evil.
  1 Comment
Habib
Habib on 2 May 2013
No, nothing prevented me from this simple modification, except I was too tired, I guess. Thanks Jose, solved.

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More Answers (2)

Matt J
Matt J on 2 May 2013
Edited: Matt J on 2 May 2013
You can define find_pw to return a 2nd argument
[F,p1]=find_pw(p,pw)
This will not conflict with FZERO. FZERO only uses the first output argument. After FZERO is finished, call the function an additional time to get the extra parameter
pw=fzero(objectivefunctionpw,[pwlim,pw]);%,options);
[~,p1] = objectivefunctionpw(pw);
There is no point trying to avoid one additional evalulation of the objective function. It's negligible overhead compared to the multiple times it gets evaluated by FZERO.
  7 Comments
Habib
Habib on 2 May 2013
Thanks. It is introduced since 2009b, and I have 2009a.
Matt J
Matt J on 2 May 2013
You're due for an upgrade!

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Alan Weiss
Alan Weiss on 2 May 2013
Make p1 global for the script, too, and it will be available everywhere you need it.
Alan Weiss
MATLAB mathematical toolbox documentation
  1 Comment
Habib
Habib on 2 May 2013
I did that, but sometimes you forget to consider this globalization in you next steps of you project. That can cause future headache for debugging.
I was wondering if there is another solution.

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