code is right but can not the a plot
显示 更早的评论
Hello, I do not what the mistake is? I'm getting the first plot. However, I have not been able to get the second plot. Not sure how to fix it. As alwyas any help will be greatly appreciated. Thanks
clear
clc
L = 1-0;
T = 0.06-0;
alpha = 1;
dx = 0.05;
dt = 0.001;
%Q = (alpha.*dt)/(dx.^2);
Q = 0.25;
N = L/dx +1;
M = T/dt + 1;
x = zeros(N,1);
t = zeros(M,1);
for i=1:N
x(i) = 0+(i-1).*dx;
end
for n=1:M
t(n) = 0+(n-1).*dt;
end
u = zeros(M,N);
u(:,1) = 2;
u(:,N) = 1;
u(1,2:N-1) = sin(pi.*x(2:N-1));
for n=1:M
for i=2:N-1
u(n+1,i) = Q.*u(n,i+1) + (1-2*Q).*u(n,i) + Q.*u(n,i-1)
end
end
figure(1)
plot (x,u(M,:)) %plot x vs u
title ('x vs u at t = 0.06')
xlabel ('x')
ylabel ('T')
grid on
figure(2)
plot(t, u(:,N-1)) %plot t vs u
title ('t vs u at x = 0.5')
xlabel ('time')
ylabel ('T')
采纳的回答
You need to redefine ‘t’ so that it matches the row size of ‘u’:
t = linspace(0, 2.5, size(u,1));
Try this —
% clear
% clc
L = 1-0;
T = 0.06-0;
alpha = 1;
dx = 0.05;
dt = 0.001;
%Q = (alpha.*dt)/(dx.^2);
Q = 0.25;
N = L/dx +1;
M = T/dt + 1;
%x = zeros(N,1);
x = linspace(0, 2.5, 5);
% t = linspace(0, 2.5, 5);
%t = zeros(M,1);
for i=1:N
x(i) = 0+(i-1).*dx;
end
for n=1:M
t(n) = 0+(n-1).*dt;
end
u = zeros(M,N);
u(:,1) = 2;
u(:,N) = 1;
u(1,2:N-1) = sin(pi.*x(2:N-1));
for n=1:M
for i=2:N-1
u(n+1,i) = Q.*u(n,i+1) + (1-2*Q).*u(n,i) + Q.*u(n,i-1);
end
end
figure(1)
plot (x,u(M,:)) %plot x vs u
title ('x vs u at t = 0.06')
xlabel ('x')
ylabel ('T')
grid on
t = linspace(0, 2.5, size(u,1)); % Redefine 't' To Match 'u'
figure(2)
plot(t, u(:,N-1)) %plot t vs u
title ('t vs u at x = 0.5')
xlabel ('time')
ylabel ('T')
EDIT — Forgot to re-run code before posting. Now run.
.
1 个评论
Torsten
2023-3-5
By changing t before plotting, u(:,N-1) is plotted at the wrong times.
更多回答（1 个）
If you compare size(t) and size(u,1), you will find that the number of elements of both vectors are not the same (they differ by one element). Thus the second plot command errors.
Replace
for n=1:M
for i=2:N-1
u(n+1,i) = Q.*u(n,i+1) + (1-2*Q).*u(n,i) + Q.*u(n,i-1)
end
end
by
for n=1:M-1
for i=2:N-1
u(n+1,i) = Q.*u(n,i+1) + (1-2*Q).*u(n,i) + Q.*u(n,i-1)
end
end
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