Alternative boundary conditions  Thomasalgorithmby Huibert Tags: boundary conditions, matlab, thomas algorithm 

#1
Dec110, 10:26 AM

P: 6

Hello,
I have to solve a diffusion equation: MatrixL * Csim(:,i+1) = MatrixR * Csim(:,i) + BoundaryConditions where Csim = concentration, j = location, i = time. Boundary conditions are of type Dirichlet (Csim = 5 at j = 1, Csim = 0 at j = end). So I used:
Matrices, first line: (1 0 . 0) * Csim(:,i+1) = (0 0 . 0) * Csim(:,i) + 5 Matrices, last line: (. . 0 1) * Csim(:,i+1) = (. . 0 1) * Csim(:,i) + 0  To solve this problem with the Thomas Algorithm, I have to write the equation as
However, it is not possible to calculate inv(MatrixR) when MatrixR(1,:)= MatrixR(end,:)= 0  So I tried to describe the boundary conditions in the folloing way : Matrices, first line: (1 0 0 . .) * Csim(:,i+1) = (1 0 0 . .) * Csim(:,i) Matrices, last line: (. . 0 0 1) * Csim(:,i+1) = (. . 0 0 1) * Csim(:,i) But that cat won't jump. So could you please help me to find what's wrong with this?  Because the problem is a littlebit complicated to explain, a longer description is in the attachment. 


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