Why do I have a never ending loop ?

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Jalyn-Rose
Jalyn-Rose 2024-3-8
评论： Torsten 2024-3-9
Not sure why my loop continues? Solving a diffusion equation for context. Continues to print out time but should stop when conditions are met.
% Define constraints
alpha = 0.001; % cm^2/s
height = 2; % cm
dx = 0.1; % cm
dt = 0.1; % s
% Boundary conditions
Tbottom = 130; % C degrees
Tcondition=60; %degrees C
% Grid spacing
npoints = int32(height/dx)+1;
% Mesh
T=ones(1,npoints)*4.0; %initial temp is 4
disp(T)
time=0;
condition=true;
while condition
time=time+dt;
fprintf('Current Time is: %f\n', time);
Tnew=ones(1,npoints);
T(1)=Tbottom;
for i=2:npoints-1
Tnew(i)=(T(i))+alpha*dt/dx/dx * (T(i+1)+T(i-1)-2*T(i));
end
i=npoints-1;
Tnew(i)=T(i)-alpha*dt/dx/dx * (T(i)-T(i-1));
Tmin=inf;
for i=1:npoints
T(i)=Tnew(i);
if T(i)<Tmin
Tmin=T(i);
end
end
if Tmin>Tcondition
condition=false;
end
end
disp(T);
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Jalyn-Rose
Jalyn-Rose 2024-3-8
I used the x=height for my grid spacing not for the boundary. My only boundaries are the T=130 and 60. T=4 is the initial temp across right side of my diffusion.
Torsten
Torsten 2024-3-8
To answer your question:
Your while loop never stops because Tnew(1) is always 1 from the setting Tnew=ones(1,npoints);, thus < Tcondition.

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Torsten
Torsten 2024-3-8
编辑：Torsten 2024-3-8
Ran in:
The initial condition at t = 0 seems to be T = 4 for all x in your code.
But you must set boundary conditions for T at x = 0 and x = 2.
At x = 0, this seems to be T = 130 for all t. But what about x = 2 ?
% Define constraints
alpha = 0.001; % cm^2/s
height = 2; % cm
dx = 0.1; % cm
nx = height/dx+1;
% Boundary conditions
Tbottom = 130; % C degrees
Tcondition=60; %degrees C
dt = 0.1; % s
nt = 5000;
T = 4*ones(nx,1);
T(1) = Tbottom;
Tnew = zeros(size(T));
condition = true;
counter = 0;
hold on
while condition
counter = counter + 1;
Tnew(1) = T(1); % T = 130 at x = 0
Tnew(2:nx-1) = T(2:nx-1)+dt*alpha/dx^2*(T(1:nx-2)-2*T(2:nx-1)+T(3:nx));
Tnew(nx) = Tnew(nx-1); %dT/dx = 0 at x = 2
T = Tnew;
condition = min(T) < Tcondition;
if counter == 500
counter = 0;
plot((0:nx-1)*dx,T)
end
end
hold off
grid on
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Jalyn-Rose
Jalyn-Rose 2024-3-8
Im uncertain of how I would see the time?

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