Why is the graph in this code becoming distorted?

Question

영택 조 2023-9-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2022912-why-is-the-graph-in-this-code-becoming-distorted

编辑： Dyuman Joshi 2023-9-19

采纳的回答： Mathieu NOE

在 MATLAB Online 中打开

%% This is the code.

n=101;

nstep=100;

long=10.0;

h=long/(n-1);

dt=0.05;

D=0.05;

f=zeros(n,1);

y=zeros(n,1);

time=0.0;

for i=1:n

f(i)=0.5*sin(2*pi*h*(i-1));

end

for m=1:nstep

plot(f,'linewidth',2);

axis([1 n -2 2])

y=f;

for ii=2:n-1

f(ii)=y(ii)-0.5*(dt/h)*(y(ii+1)-y(ii-1)+D*(dt/h^2)*(y(ii+1)-2*y(ii)+y(ii-1)));

end

f(n)=y(n)-0.5*(dt/h)*(y(2)-y(n-1))+D*(dt/h^2)*(y(2)-2*y(n)+y(n-1));

time=time+dt;

title(sprintf('time = %3.2f',time))

pause(0.2)

end

As a result of running this code, the graph becomes distorted from the right end and stretched as 'time' increases. Is there something wrong that is causing this?

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Answer 1

Mathieu NOE 2023-9-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2022912-why-is-the-graph-in-this-code-becoming-distorted#answer_1313192

在 MATLAB Online 中打开

hello

maybe this ? I simply corrected one of your equation (looking at the one that follows , assumming the second was correct ) because there is a difference where you put your parenthesis

%% This is the code.
n=101;
nstep=100;
long=10.0;
h=long/(n-1);
dt=0.05;
D=0.05;
f=zeros(n,1);
y=zeros(n,1);
time=0.0;
i=1:n;
f=0.5*sin(2*pi*h*(i-1));
for m=1:nstep
    
     plot(f,'linewidth',2);
     axis([1 n -2 2])
     y=f;
     
     for ii=2:n-1
%         f(ii)=y(ii)-0.5*(dt/h)*(y(ii+1)-y(ii-1)+D*(dt/h^2)*(y(ii+1)-2*y(ii)+y(ii-1)));
        f(ii)=y(ii)-0.5*(dt/h)*(y(ii+1)-y(ii-1))+D*(dt/h^2)*(y(ii+1)-2*y(ii)+y(ii-1)); % correction based on the equation 2 lines below
     end
     f(n)=y(n)-0.5*(dt/h)*(y(2)-y(n-1))+D*(dt/h^2)*(y(2)-2*y(n)+y(n-1));
     time=time+dt;
     title(sprintf('time = %3.2f',time))
     pause(0.2)
     
end