Slider Code problem with axes

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Hassan Bosha
Hassan Bosha on 16 Feb 2019
Commented: Rik on 20 Feb 2019
this an example of a slider to control movement on axes
a = get (handles.slider2,'Value')
x = 0:0.1:50;
y = sin (x*a);
plot (handles.axes1,x,y)
and this me trying to apply the example
function slider2_Callback(hObject, eventdata, handles)
% hObject handle to slider2 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'Value') returns position of slider
% get(hObject,'Min') and get(hObject,'Max') to determine range of slider
load ('100m.mat')
a = get(handles.slider2,'Value');
x = 0:0.1:50;
ECGsignal = (val - 1024 )/200;
y = ECGsignal*x*a;
plot (handles.axes1,x,y)
what is the problem in my code ?
Hassan Bosha
Hassan Bosha on 19 Feb 2019
can you show me a example code for it ?

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Accepted Answer

Rik on 19 Feb 2019
Instead of scaling the data, this code changes the axis limits.
%generate some data and set the x window size
%make the GUI
clf(h.f)%make sure the figure is empty, not needed if you use h.f=figure;
'Position',[0.1 0.3 0.8 0.6]);
'Position',[0.1 0.1 0.8 0.1],...
%make the plot
plot(x,y,'Parent', the plot itself
%set(,'YLim',[min(y) max(y)])%fix the y-axis to specific values
set(,'YLim',[-1 1])%fix the y-axis to specific values
sliderCallback(h.f)%initialize the x-axis
function sliderCallback(obj,evnt)
set(,'XLim',[-0.5 0.5]*handles.xwindow_size+a)
Rik on 20 Feb 2019 should be replaced by whatever the handle for your axes object is, likely handles.axes1. And again, you have put code in your callback that loads data. That is something you should put in the createFcn of your GUI (or is it called startFcn?). A callback should be treated as an interupt: as little work as possible should be done in them. A callback will trigger often, every 200 ms you spend on loading that mat introduces 200 ms of delay.
% --- Executes on slider movement.
function slider4_Callback(hObject, eventdata, handles)
set(,'XLim',[-0.5 0.5]*handles.xwindow_size+a)

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More Answers (1)

Yair Altman
Yair Altman on 17 Feb 2019
In your example, both val and x are not scalars. When you multiply vectors/matrices in Matlab using the * operator, Matlab uses linear algebra rules to multiply the data. This causes an error because the two variables do not match in their size as required by linear algebra multiplication rules (that the number of rows in one multiplicant is equal to the number of columns in the other).
What you probably wanted to do instead was to multiple each element of val by the corresponding element in x (assuming that they are both vectors of the same size) - this is done with element-wise multiplication (.*) :
y = ECGsignal.*x*a;
  1 Comment
Hassan Bosha
Hassan Bosha on 18 Feb 2019
still same problem , i just need a code to move the slider on zooming

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