The plot of this discontinous values does not work.

Dear Matlab Community,

I got a problem plotting this discontinous geometry. There are no erros, but The plot is empty, just filled with some dots, that are even hard to realize :-( I really need to plot with x defined as a vector using linspace, like I did. I have no clue how to solve this problem. I would be very thankful if someone could help me out.

Thank you! Stefan

Here is the code I try to plot:

clc
clear all
close all

%Parameter:
R=2;
h=1; 
L=10;
B = 5;
x=linspace(0.0,(2*R+L),100);
hmin = h/2; 

if (x < R)
 y2 = (R+hmin)-sqrt((R+hmin)^2-((R+hmin)^2-R^2+(x-R).^2));
 y2_neg = -y2;
elseif (x > (L+R))
 y2 = (R+hmin)-sqrt((R+hmin)^2-((R+hmin)^2-R^2+(x-R).^2));
 y2_neg = -y2;
 else
 y2 = hmin;
 y2_neg = -y2;
end

plot(x,y2,x,y2_neg);
grid on
title('Geometrie der Gelenkkontur')
xlabel('s = [0:L]')
ylabel('H(x)')
axis equal

Answer 1

[Erik S.]

I send you a file, is it the result you need?

[Stefan Henning]

Thank you very much, this works perfectly fine!

I had to correct my code in here:

elseif (x(n) > (L+R))
 y2(n) = (R+hmin)-sqrt((R+hmin)^2-((R+hmin)^2-R^2+(x(n)-L-R).^2));

where I changed x(n)-R to x(n)-L-R and now I ged the exact correct solution. Thanks a lot for helping!

[Erik S.]

Great! Glad I could help! :) Pls Click on the Accept Answer button :)

[Stefan Henning]

Sure :) Again, thanks a lot!

Answer 2

[Erik S.]

Your y2 and y2_neg variables are not vectors, only scalars You can make a loop and compute the y2 and y2_neg for each value of x instead

[Stefan Henning]

Thanks for the quick answer! I changed it to:

for x=0:0.1:(L+2*R)
if (x < R)
 y2 = (R+hmin)-sqrt((R+hmin)^2-((R+hmin)^2-R^2+(x-R).^2));
 y2_neg = -y2;
elseif (x > (L+R))
 y2 = (R+hmin)-sqrt((R+hmin)^2-((R+hmin)^2-R^2+(x-R).^2));
 y2_neg = -y2;
 else
 y2 = hmin;
 y2_neg = -y2;
end
plot(x,y2,x,y2_neg);
grid on
title('Geometrie der Gelenkkontur')
xlabel('s = [0:L]')
ylabel('H(x)')
axis equal
end

But now I get Errors and an empty plot. I have to say I am new to matlab and do not find the problem here.. Thanks!

Answer 3

[Erik S.]

There are a couple of issues. First you get complex numbers ( at least I get it when I run your code) so somehow you take the sqrt of a negative value. Secondly you overwrite your plot in every iteration. I would recommend to create vectors inside the loop (i.e. make y2 and y2_neg vectors) and run the plotting command outside the loop