The plot of this discontinous values does not work.

Question

Stefan Henning 2015-2-18

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评论： Stefan Henning 2015-2-18

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

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Answer 1

Erik S. 2015-2-18

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helper.m

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

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Erik S. 2015-2-18

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

Stefan Henning 2015-2-18

Sure :) Again, thanks a lot!

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Answer 2

Erik S. 2015-2-18

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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

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Stefan Henning 2015-2-18

在 MATLAB Online 中打开

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!

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Answer 3

Erik S. 2015-2-18

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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