How to change diagonal, subdiagonal and superdiagonal values with respect time while using loop and conditional statement?

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Yanni
Yanni 2023-3-14
编辑： Yanni 2023-4-29
xmax=1; ymax=7; m=20; n=29;
dx=xmax/m; dy=ymax/n; dt=0.2;
UOLD=zeros(m,n);VOLD=zeros(m,n);
A=zeros([1,m]);
B=A;
C=A;
while dt<tmax
for j=1:n
for i=1:m
if j>i
C(i)=((dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %superdiagonal
elseif i>j
A(i)=((-dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %sub diagonal
elseif i==j
B(i)=1+((dt*UOLD(i,j))/(2*dx))+(dt/(dy^2)); %main diagonal
end
end
end
dt=0.2+dt;
end
  4 个评论
显示 2更早的评论
Dyuman Joshi
Dyuman Joshi 2023-3-14
"You changing that matrix size only."
How else are you going to get the values on diagonals?
What are the expected outputs?
Dyuman Joshi
Dyuman Joshi 2023-3-15
I didn't understand what you meant by your comment below my response.
Also, you did not answer my questions - How else are you going to get the values on "diagonals"?
What are the expected outputs? Please provide exactly what the values of A, B and C you want to get.

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采纳的回答

Dyuman Joshi
Dyuman Joshi 2023-3-15
编辑：Dyuman Joshi 2023-3-15
Ran in:
xmax=1; ymax=7; m=20; n=29; tmax=100; nt=500;
dx=xmax/m; dy=ymax/n; dt=tmax/nt;
UOLD=zeros(m,n);VOLD=zeros(m,n);
A=zeros(m,m);
B=A;
C=A;
while dt<tmax
for j=1:n
for i=1:m
if j>i
C(j-1,j)=((dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %superdiagonal
elseif i>j
A(i,i-1)=((-dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %sub diagonal
elseif i==j
B(i,j)=1+((dt*UOLD(i,j))/(2*dx))+(dt/(dy^2)); %main diagonal
end
end
dt=0.2+dt;
end
end
A
A = 20×20
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -847.8653 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -849.5816 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -851.2980 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -853.0143 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -854.7306 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -858.1633 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -859.8796 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -861.5959 0 0 0 0 0 0 0 0 0 0 0
B
B = 20×20
1.0e+03 * 1.6967 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7002 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7036 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7070 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7105 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7173 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7208 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7242 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7276 0 0 0 0 0 0 0 0 0 0
C
C = 28×29
0 -849.5816 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -851.2980 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -853.0143 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -854.7306 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -858.1633 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -859.8796 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -861.5959 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -863.3122 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -865.0286 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

更多回答（1 个）

Oguz Kaan Hancioglu
Ran in:
As @Dyuman Joshi mentioned, the problem statement is not clear. However vectors don't have diagonal. Please change the A,B, and C as a matrix and use correct indeces. I think it solves your problem.
xmax=1; ymax=7; m=20; n=29; tmax=100; nt=500;
dx=xmax/m; dy=ymax/n; dt=tmax/nt;
UOLD=zeros(m,n);VOLD=zeros(m,n);
A=zeros([m,n]);
B=A;
C=A;
while dt<tmax
for j=1:n
for i=1:m
if j>i
C(i,j)=((dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %superdiagonal
elseif i>j
A(i,j)=((-dt*VOLD(i,j))/(4*dy))-(dt/(2*(dy^2))); %sub diagonal
elseif i==j
B(i,j)=1+((dt*UOLD(i,j))/(2*dx))+(dt/(dy^2)); %main diagonal
end
end
end
dt=0.2+dt;
end
A
A = 20×29
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
B
B = 20×29
1.0e+03 * 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.7139 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C
C = 20×29
0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 0 0 0 0 0 0 0 0 0 0 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469 -856.4469

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