GUI derivative calculator, issues with coding portion

Hello All,

I am trying to do my final MATLAB project and it involves creating a GUI that can handle second order differential equations. Firstl I have been trying to figure out how to make a simple derivative GUI calculator, one that can handle something from the user say 4X and when a button is pushed will spit out its derivite, 4. So far I have made the GUI and have been trying to add some code. I am new to MATLAB and some of the errors are confusing. I will post parts of the code along with my logic below:

let me define some things to make it easier to understand.

I have an edit text box whose tag line is FCN (this is the box the user will enter the derivative that needs to be taken)

I have a push button whose tag line is equal

I have a static text box whose tag line is first (this is where the answer will pop out)

I wrote a few lines of code under the equal callback:

function equalPushButton_Callback(hObject, eventdata, handles)
% hObject    handle to equalPushButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
syms x
a=get(handles.FCN,'string'));
b=str2sym(diff(a)); %Or b=double(b)? 
set(handles.first,'string',sym2num(b));

I am wondering if someone can steer me in the right direction

Thanks

[Murugan C]

Hi William Fantin,

Can you please post your error what got in matlab command window.

If possible, Can you please attach your full code.?

[William Fantin]

Sure, so i did some more research and now my code is different. I have my program where if I type in x it will give the derivative of 1. But when I type say 4*x it will give an error. Heres the code:

function varargout = Test5(varargin)
% TEST5 MATLAB code for Test5.fig
%      TEST5, by itself, creates a new TEST5 or raises the existing
%      singleton*.
%
%      H = TEST5 returns the handle to a new TEST5 or the handle to
%      the existing singleton*.
%
%      TEST5('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in TEST5.M with the given input arguments.
%
%      TEST5('Property','Value',...) creates a new TEST5 or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before Test5_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to Test5_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help Test5

% Last Modified by GUIDE v2.5 05-May-2019 12:47:09

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @Test5_OpeningFcn, ...
                   'gui_OutputFcn',  @Test5_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before Test5 is made visible.
function Test5_OpeningFcn(hObject, eventdata, 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 Test5 (see VARARGIN)

% Choose default command line output for Test5
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes Test5 wait for user response (see UIRESUME)
% uiwait(handles.figure1);


% --- Outputs from this function are returned to the command line.
function varargout = Test5_OutputFcn(hObject, eventdata, 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;



function FCN_Callback(hObject, eventdata, handles)
% hObject    handle to FCN (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of FCN as text
%        str2double(get(hObject,'String')) returns contents of FCN as a double


% --- Executes during object creation, after setting all properties.
function FCN_CreateFcn(hObject, eventdata, handles)
% hObject    handle to FCN (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end


% --- Executes on button press in equalPushButton.
function equalPushButton_Callback(hObject, eventdata, handles)
% hObject    handle to equalPushButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
f=get(handles.FCN,'String')'
syms x
der=diff(f,x)
set(handles.first,'String',char(der));

Thanks!!

[Murugan C]

Hi

I think, we shouldn't use "syms" for derivative .we have create one more edit box for getting derivative as like below,

f = get(handles.FCN,'String');

x = str2double(get(handles.derivative,'String')); % derivative order

der=diff(f,x);

set(handles.first,'String',char(der));

Answer 1

[Raag]

Hi William,

The issue seems to be arising from using the ‘syms’ function within the callback. This function modifies the base workspace in a manner that is incompatible with the static nature of the GUI workspace. As a workaround, ‘str2sym’ function can be used to resolve the workspace issue.

Follow these steps to resolve the workspace issue:

• Use ‘str2sym’ function: which converts the input string into a symbolic expression without the need to define ‘syms x’. Usage of this function resolves the workspace issue, while taking input from the user.
• Differentiation: use ‘diff(f_sym, 'x')’ to compute the derivative of the expression, where ‘f_sym’ is the symbolic form of the user's input.

Here is an example code snippet for the above-mentioned workaround:

function equalPushButton_Callback(hObject, eventdata, handles) 

    % Get the input from the edit text box 

    f = get(handles.FCN, 'String'); 

  

    try 

        % Convert the input string to a symbolic expression 

        f_sym = str2sym(f); 

  

        % Calculate the derivative with respect to 'x' 

        der = diff(f_sym, 'x'); 

  

        % Display the derivative in the static text box 

        set(handles.first, 'String', char(der)); 

    catch 

        % Display an error message if the input is invalid 

        set(handles.first, 'String', 'Error: Invalid input'); 

    end 

end

For more information on ‘str2sym’ function, refer to this documentation:

https://www.mathworks.com/help/symbolic/str2sym.html