fzero function, additional output needed

Question

Habib 2013-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/74336-fzero-function-additional-output-needed

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.

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Answer 1

José-Luis 2013-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/74336-fzero-function-additional-output-needed#answer_84189

在 MATLAB Online 中打开

Is there anything preventing you from modifying find_pw() to return p1 as well?

function [F,p1]=find_pw(p,pw)

Globals are evil.

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Habib 2013-5-2

No, nothing prevented me from this simple modification, except I was too tired, I guess. Thanks Jose, solved.

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Answer 2

Matt J 2013-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/74336-fzero-function-additional-output-needed#answer_84190

编辑：Matt J 2013-5-2

在 MATLAB Online 中打开

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.

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Habib 2013-5-2

在 MATLAB Online 中打开

your reply raised another question for me. what does ~ mean as an input or output argument? I have seen it in example gui's and I dont know what it is. and when i ran the gui, Matlab gave error on ~. This is a part of that code:

% --- Executes just before casio is made visible.
function casio_OpeningFcn(hObject, ~ , handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to casio (see VARARGIN)
% Choose default command line output for casio
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes casio wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = casio_OutputFcn(~, ~, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(~, ~, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB

Habib 2013-5-2

Thanks. It is introduced since 2009b, and I have 2009a.

Matt J 2013-5-2

You're due for an upgrade!

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Answer 3

Alan Weiss 2013-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/74336-fzero-function-additional-output-needed#answer_84182

Make p1 global for the script, too, and it will be available everywhere you need it.

Alan Weiss

MATLAB mathematical toolbox documentation

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Habib 2013-5-2

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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fzero function, additional output needed

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fzero function, additional output needed

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