Thomas algorithm - tridiagonal matrix

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Cesar Cardenas
Cesar Cardenas 2023-3-1
评论： Cesar Cardenas 2023-3-2
Is there any other way to code and solve the tridiagonal matrix? the idea would be to try to get the plot shown. Matlab beginner, so, no sure how to do it. Any help will be greatly appreciated. Thanks
clear
cm=1/100;
delta = 1*cm;
nu=1e-6;
Uinf=1;
H=2*delta;
y=linspace(0,H,40);
u=Uinf*erf(3*y/delta);
dy=mean(diff(y));
dx=100*dy;
Q=nu*dx/Uinf/dy^2;
a=-Q;
c=-Q;
b=1+2*Q;
N=length(y)-2;
M = diag(b*ones(1,N)) + diag(c*ones(1,N-1),1) + diag(a*ones(1,N-1),-1);
%Constant Ue
Ue = @(x) Uinf;
u = u(2:end-1);
x=0;
uall=[0,u,Ue(x)];

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采纳的回答

Torsten
Torsten 2023-3-2
编辑：Torsten 2023-3-2
Ran in:
clear
cm=1/100;
delta = 1*cm;
nu=1e-6;
Uinf=1;
H=2*delta;
y=linspace(0,H,40);
u=Uinf*erf(3*y/delta);
dy=mean(diff(y));
dx=100*dy;
Q=nu*dx/Uinf/dy^2;
a=-Q;
c=-Q;
b=1+2*Q;
N = length(y);
M = diag(b*ones(1,N)) + diag(c*ones(1,N-1),1) + diag(a*ones(1,N-1),-1);
M(1,:) = [1,zeros(1,N-1)];
M(end,:) = [zeros(1,N-1),1];
%Constant Ue
Ue = @(x) Uinf;
u = u(2:end-1);
x=0;
uall=[0,u,Ue(x)];
sol = M\uall.';
plot(y,sol)
grid on
  5 个评论
显示 3更早的评论
Torsten
Torsten 2023-3-2
You can assign values to certain elements in a matrix by using a loop. But if the above line to define M is correct, it's elegant, isn't it ? Why do you want to define it differently ?
Cesar Cardenas
Cesar Cardenas 2023-3-2
Right thank you, just wanted to have a different version. Thanks

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