How to import equation from GUI to functions?

I want the user to be able to insert his own equation (e.g. a*x.^2 + b*x + c) to be used to plot the function. I have already defined the variables a, b and c (to which it will be limited) and have everything working if I put y=*equation* in the .m file. How would I point Matlab towards using what is in the GUI text box (the equation input) to answer y=... and plot accordingly?

[Tom]

Are there 3 editboxes in the GUI (for a, b and c)? And where does x come from?

[John]

Yeah, 3 seperate boxes. x is defined as an interval specified on the gui:

x= str2num(get(handles.x_lower, 'String' )):str2num(get(handles.x_upper, 'String' ));

Answer 1

[Matt Fig]

Here is an example. Paste the code into a new M-file and run it. In the text box you can enter an equation which depends on x, a, b and c. The values of a, b and c are hardwired as you indicate above.

function [] = plot_func()
% Help
S.fh = figure('units','pixels',...
              'position',[300 300 200 130],...
              'menubar','none',...
              'name','plot_func',...
              'numbertitle','off',...
              'resize','off');        
S.ed = uicontrol('style','edit',...
                 'unit','pix',...
                 'position',[10 70 180 40],...
                 'string','Enter func of x,a,b,c',...
                 'fontsize',10);
S.pb = uicontrol('style','push',...
                 'unit','pix',...
                 'position',[10 20 180 35],...
                 'string','plot it!',...
                 'fontsize',14);
set(S.pb,'callback',{@pb_call,S})  % Set callback.
uicontrol(S.ed)

function [] = pb_call(varargin)
% Callback for pushbutton.
S = varargin{3};  % Get the structure.

func = vectorize(inline(get(S.ed,'string'),'a','b','c','x'));
x = 0:.01:1;
figure
plot(x,func(2,3,4,x)) % a=2,b=3,c=4 - hardwired.

[John]

Wow... Just so you know, I'm new at this. What I'm doing now, is using "guide" to create my gui and using input values like this:

a = str2num(get(handles.a_value, 'String' ));

with everything under function plot_Callback.

I don't know how to integrate your code above with how I'm doing it - it probably diffirs because I use the gui editor instead of raw code...?

Isn't there a way to just 'copy' the string from a text box in the gui into the code because everything works fine if I define y myself (e.g. y = a*x.^2 + b*x + c in my code). So if I can say y = whatever is in the string of equation text box, wouldn't that work?

Also, for now I'm not bothered with efficiency, e.g. using varargin, because I haven't really looked up on how it diffirs from what I'm doing now and this is a very small project. Thanks for the help so far! Still trying to build my program around your code now.

[Matt Fig]

If you are using GUIDE, then you will want to have something that triggers the plot, like a pushbutton. In the callback for the pushbutton, you do what you did but add to it:

a = str2num(get(handles.a_value, 'String' ));
b = str2num(get(handles.b_value, 'String' ));
c = str2num(get(handles.c_value, 'String' ));
y = vectorize(inline(get(handles.y,'string'),'a','b','c','x'));
x = 0:.01:1;
figure
plot(x,y(a,b,c,x))

[Walter Roberson]

PRAJWAL GOWDA HM comments to John:

can u send this program...