Limit x-axis to specific values in GUI

Hello, I have a pushbutton which plots any function the user typed in an editable text. I also have two sliders, slider1 and slider2, who should dictate the limits of the x-axis of my plot. So slider1 should give the lower bound and slider2 the upper bound of the x-axis to display. My code doesn't work, I hope someone can help me with this:

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (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.edit1, 'string') 
x = 0:0.1:1;  
m = get(handles.slider1, 'Value')
n = get(handles.slider2, 'Value')
set(handles.axes1, 'XLim', [m, n])
axes(handles.axes1)
plot(eval(f))

Thank you!

[Adam]

You didn't say in what way your code doesn't work.

Generally though you should set axes limits after plotting rather than before because many plotting functions override the current limits and set their own auto limits.

[Robert Eisenbecker]

Oh sorry, yes, the limits of the x-axis do change according to the sliders. But the plot is not showing any more, the axis is empty.

[Adam]

Then it sounds as though you are setting the limits to be outside of the valid range of the plot.

[Robert Eisenbecker]

If I for example type in just the function x, which is a 45° line from the origin, then the graph still doesn't show up. The limits of my sliders are between 0 and 1... If I don't touch the sliders, my functions are plotted perfectly fine, as soon as I change the sliders they disappear.

[Adam]

It's hard to give any intelligent answer if you don't show what the function is that is being passed to eval and what your sliders are being set to. 'x' is not a function so no wonder it does not plot anything. You have to plot actual values when using plot, you can't just give it an equation.

How do you know the values of your sliders after moving them? Are they (correctly) attached to edit boxes or are you just guessing the values?

[Robert Eisenbecker]

I'm sorry for being too vague, I will try to explain it better now:

I have an edit box in which the user has to insert a function. After pushing a button, the function in the edit box is plotted into axes1. This works perfectly fine. My next task is to include two sliders m and n which determine the range of the x axis [m n]. So, for example, if I type x in the edit1 box, then it will plot f(x) = x into my axes1. Or if I want to show f(x) = x only between 0.1 and 0.5 on the x axis, I adjust the sliders and then after pushing the button, the plot will be updated accordingly.

Because plotting the functions works, I don't see why I cannot give plot() an equation. It correctly plots everything I put into the editbox, e.g. sin(x), x.^2+x*2, etc. I have defined x to be x = 0:0.1:10. I set the sliders to be between 0 and 1. I know the values of the sliders because they show up in the command window and they seem to be correct.

[Robert Eisenbecker]

Nevermind, I have found a solution using ezplot, where I can easily edit the xmin and xmax parameters. Thank you for your help still!

Answer 1

[Jan]

Avoid setting the current axes actively. Better define the parent object to draw in:

% Instead of
axes(handles.axes1)
plot(eval(f)) 
% use
plot(handles.axes1, eval(f))

Is the 'NextPlot' property of the axes set to 'add'? This is equivalent to hold('on'). Otherwise a plot() command might reset the limits.

If the plot vanishes when the sliders are used, it sounds, like the problem is in the slider's callback, not in the one of the pushbutton.

[Robert Eisenbecker]

I have found a way with ezplot, thank you for your answer still!