MATLAB: In a GUI, How to accept user input and turn string into a function? ex. 3x^2 +2x -5

guimatlab guistring to function

% — Executes on button press in Graph.

function Graph_Callback(hObject, eventdata, handles)

syms x y;

userInput = get(handles.user1,'String');

fun = @(x) userInput;

x=0:10;

y = fun(x);

axes(handles.axes1);

plot(x,y);

xlabel('x'); ylabel('y');

guidata(hObject,handles);

   fun = str2func( ['@(x)' userInput])

x=str2num(get(handles.Txo, 'string'));
y=str2num(get(handles.Tyo, 'string'));

Those will result in x and y being defined as numeric values (probably, but not always. str2double() would be better.)

syms x y;

Those are equivalent to

x = sym('x');
y = sym('y');

so whatever numeric values x and y had will be erased and replaced with symbolic values.

switch opcion
    case 1 %Método de Euler
        n=(xf-x)/h;

x is symbolic so n ends up symbolic

        for i=1:n+1

with n being symbolic, 1:n+1 tries to use the : operator with a symbolic upper bound, which fails.

Change

num2str(set(handles.solution, 'string', diffyEQ));

set(handles.solution, 'String', char(diffyEQ));