# how to plot discontinuous functions in matlab?

306 views (last 30 days)
rr mm on 6 Sep 2015
Answered: Daniel Garside on 2 Mar 2018
Hi everyone!
I want to plot a simple floor function without connections between points in separate steps. I do this in maple with discont=true property. I used scatter function but I want to have straight line instead of circles. how can I do the same in matlab?

the cyclist on 6 Sep 2015
Here is an example that sounds like what you want:
figure
x = 1:10;
y = 3 + (x>5);
h = plot(x,y,'.');
set(h,'MarkerSize',24)
ylim([2 5])
rr mm on 6 Sep 2015
Dear friend,
it does the same scatter function, the result must be like this image.
thanks

Walter Roberson on 6 Sep 2015
Every function sampled at a finite number of points is effectively discontinuous and there is no way to automatically tell from the finite list of sampled points whether two adjacent points "should" be joined or not.
You need to either add some intelligence about where the discontinuities are, or you need to process them symbolically by calling into MuPad's discont() function
syms x
feval(symengine, 'discont', floor(x), sym('x = 1..5'))
and then somehow process the discontinuity set in constructing your numeric plot.
If you were to work in a MuPAD notebook, you could use http://www.mathworks.com/help/symbolic/mupad_ref/plot-function2d.html as that has discontinuity processing turned on by default. I have never seen an answer for what happens if you try to feval() a MuPAD plot from the MATLAB level.

Daniel Garside on 2 Mar 2018
If you just want the visuals something like this works:
for i=1:10
plot([i, i+1],[i,i])
end