Error: indexing must appear last in an index expression.

i got the following error when i tried to run the code I wrote

 Error using str2func
 Error: ()-indexing must appear last in an index expression.

 Error in Spro>VbR_button_Callback (line 836)
    V=str2func(['@(t)
    ',char(diff(sym(regexprep(char(XFunction_current),'^@\(t\)',''))))]);

 Error in gui_mainfcn (line 96)
        feval(varargin{:});

 Error in Spro (line 42)
    gui_mainfcn(gui_State, varargin{:});

 Error in
 @(hObject,eventdata)Spro('VbR_button_Callback',hObject,eventdata,guidata(hObject))

 Error while evaluating uicontrol Callback

Note: In my code the variable x is equal to the end value of the before last function I enter in .The new function I give or enter in the uitable can be depending on x ,but it should have just one input argument t , so i created x , so when I give x it will be as a number and not variable .

 Tabledata=get(handles.Xtable,'data');
 Positiondata=XTableCurrentdata(:,1);  % matrix of Strings (functions)
 Timedata=XTableCurrentdata(:,2);      %Matrix of Time intervals 

 n=size(Tabledata,1);
 for i=1:n

    Tcurrent = str2num(Timedata{i,1}); %t2 end time of the current function [t1 t2]
    EndTime_current=max(Tcurrent); 

    Xfunc_current= str2func(['@(t,x)' Positiondata{i,1}]);    
    X(1)=0;
    X(i+1)=Xfunc_current(EndTime_current,X(i));
    XFunction_current=@(t) Xfunc_current(t,X(i));

    V=str2func(['@(t) ',char(diff(sym(regexprep(char(XFunction_current),'^@\     
    (t\)',''))))]);
    ...

[Amit]

I am sorry Sam. My answer was wrong and very wrong. Thats why I deleted it. Your code is right upto the first str2func. The issue is in second str2fun. I donot know much of symbolic toolbox but there will be many here who can help you.

[per isakson]

See: http://www.mathworks.com/matlabcentral/answers/87710#answer_97292

Answer 1

[Walter Roberson]

You would be better off using anonymous functions to capture the value of the variable instead of trying to convert the variable to a specific value in a string and re-converting the string to a function.

You should also consider using func2str() instead of the char() stuff you are using.

As you are using sym() you are using the symbolic toolbox. A better way to do diff() of a function handle F(x), rather than stripping off the anonymous header from char() of the function handle and diff()'ing sym() of that, is to use something like

sym t
diff(F(t),t)

You can then use matlabFunction to convert that symbolic expression back to a function handle.

[Elia]

it works thank you , but I used 'str2func(['@(t)' char(F)])' to convert the symbolic expression back to a function handle. because I got error with using matlabFunction when the the function is a polynomial with degree 1 or a constant.