Problem in running GUI

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Suraj Gurav
Suraj Gurav on 15 Oct 2017
Edited: Stephen on 26 Oct 2017
I am creating a GUI for Newton Raphson method. The code I wrote works well but when it comes to GUI it shows strange error. following is the error. Could anyone tell me how to get solved this error.
y =
1×1 cell array
Error using eval Must be a string scalar or character vector.
Error in newtonraphson>pushbutton1_Callback (line 109) yy=eval(y)
Error in gui_mainfcn (line 95) feval(varargin{:});
Error in newtonraphson (line 42) gui_mainfcn(gui_State, varargin{:});
Error in>@(hObject,eventdata)newtonraphson('pushbutton1_Callback',hObject,eventdata,guidata(hObject)) Error while evaluating UIControl Callback.
I have attached the .fig file also, so that you can check it.
Stephen on 18 Oct 2017
You are creating a GUI for the Newton-Raphson method, and you need slow, buggy, totally inefficient eval ? Why not simply stick to faster, simpler, and much more efficient numeric calculations ?

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Accepted Answer

OCDER on 16 Oct 2017
Edited: OCDER on 16 Oct 2017
Don't use eval because it's way too powerful of a function that leads to issues and is slow. It's like using a chain saw to cut a birthday cake (doing a simple task) - it works, but you'll end up with a big mess (unable to debug), it was way too dangerous to use (can overwrite / delete any var or files), and you just might destroy the table holding the cake (you'll have to rebuild your program and unlearn the eval habit) ...
To fix, rewrite your code at pushbutton1_Callback (line 109):
instead of:
yy = eval('sin(x)') or yy = eval(y{1})
just do:
yy = sin(x)
or if it's not always a sine function, then:
fh = str2func(['@(x)' y{1}])); %creates a function handle like @(x) sin(x)
yy = fh(x); %evaluates sin(x)
Stephen on 18 Oct 2017
"Finally the GUI worked fine with the eval command"
I have written hundreds of MATLAB GUIs from scratch, and never needed to use slow, buggy, awful eval or assignin. Note that <using eval to evaluate symbolic equations is the wrong tool for that task, as Steven Lord explains here:
Also worth reading:
You might like to consider the advice that people are giving you.

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