MATLAB Answers

Plot multiple subintervals in one figure

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Joakim Karlsson
Joakim Karlsson 9 Nov 2017
댓글: Rik 11 Nov 2017
Hello all. Probably quite an easy problem but I am stuck.
f=@(t,u)-u+sin(5*t)+cos(2*t);
a=0; b=5; ua=2; % begynnelsevillkor
t=linspace(a,b,15); u=linspace(-2,2,15);
riktningsfaelt(f,t,u);
N=10; h=(b-a)/N; %steglängd
T=linspace(a,b,N+1); U=zeros(size(T));
U(2)=ua; %enligt begynnelsevillkor
for n=1:N
U(n+1)=U(n)+h*f(T(n),U(n)); % Eulers metod
end
plot(T,U)
So what I want to do is plot but with different N values in the same figure. I have tried "hold on" then set a new N value but it doesn't work. Lets say I want to plot N=10 and N=100 in the same figure, how do I do that??

  댓글 수: 2

Rik
Rik 9 Nov 2017
You did run the plot command another time after the hold on?
Joakim Karlsson
Joakim Karlsson 10 Nov 2017
Yes I did but the script just computed the first thing again. So it didn't really change anything.

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Mischa Kim
Mischa Kim 10 Nov 2017
편집: Mischa Kim 10 Nov 2017
Joakim, is this what you had in mind?
f=@(t,u)-u+sin(5*t)+cos(2*t);
a=0; b=5; ua=2; % begynnelsevillkor
t=linspace(a,b,15); u=linspace(-2,2,15);
% riktningsfaelt(f,t,u);
for N = 10:10:100
h=(b-a)/N; %steglängd
T=linspace(a,b,N+1);
U=zeros(size(T));
U(2)=ua; %enligt begynnelsevillkor
for n=1:N
U(n+1)=U(n)+h*f(T(n),U(n)); % Eulers metod
end
plot(T,U)
hold on
end

  댓글 수: 4

표시 이전 댓글 수: 1
Mischa Kim
Mischa Kim 10 Nov 2017
Simple enough. Replace the for command by
for N = [10,100,1000]
The code in my first answer above creates essentially the same graph, just with 10 plots vs 3.
Joakim Karlsson
Joakim Karlsson 10 Nov 2017
Yeah this works very well actually. Now I'd just like to set my own colours if that is possible since its hard to look at it when one is yellow and one is orange haha.
Rik
Rik 11 Nov 2017
Save the handles to the line objects (output of plot function) and you can set the color. (or just use a cell array with the color string inside the for-loop)

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