Issue with Matrix Dimensions

6 次查看（过去 30 天）
Nilesh Naik
Nilesh Naik 2022-2-6
回答： Voss 2022-2-6
Hello All,
I am trying to run this code for some calculation but I seem be getting an disnion mismatch error. I have tried revisiting this code again and aagain but not able to find what I am missing. I am coming to the community to understand what is that I am missing Appreciate your help.
M=44;
N=11;
N1=6;
h=0.1;
Re=100;
for i=1:M
for j=1:N
u(i,j)=0;
v(i,j)=0;
si(i,j)=0;
om(i,j)=0;
end
end
for j=1:N1
y=(j-1)*h;
u(1,j)=-1.5+6*y*y;
si(1,j)=-0.5-1.5*y+2*y*y*y;
om(1,j)=-12*y;
end
for j=N1+1:N
y=(j-1)*h;
u(1,j)=-18*y*y+12*y-1.5;
si(1,j)=-6*y*y*y+6*y*y-1.5*y-0.5;
om(1,j)=36*y-12;
end
for i=(2:M-1)
si(i,N)=-0.5;
end
for j=(1:N)
y=(j-1)*h;
si(M,j)=-0.25+y*y*y-0.75*y;
u(M,j)=-0.75+3*y*y;
om(M,j)=-6*y;
end
for ite=(1:500)
for i=(2:M-1)
om(i,1)=-u(i:2)/h;
om(i,N)=u(i:N-1)/h;
end
for i=(2:M-1)
for j=(2:N-1)
si(i,j)=(si(i-1,j)+si(i+1,j)+si(i,j-1)+si(i,j+1)+om(i,j)*h*h)/4;
end
end
for i=(2:M-1)
for j=(2:N-1)
omx=(om(i+1,j)-om(i-1,j))/(2*h); %this line seems to be having an issue.
omy=(om(i,j+1)-om(i,j-1))/(2*h);
con=u(i,j)*omx+v(i,j)*omy;
om(i,j)=(((om(i-1,j)+om(i+1,j)+om(i,j-1)+om(i,j+1))-Re*con*h*h)/4);
end
end
end
for i=(1:M)
for j=(1:N)
u1(i,j)=1.5-6*y*y+u(i,j);
v1(i,j)=v(i,j);
end
end

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采纳的回答

William Rose
William Rose 2022-2-6
@Nilesh Naik,
The error occurs at lines
for ite=(1:500)
for i=(2:M-1)
om(i,1)=-u(i:2)/h; %error here
om(i,N)=u(i:N-1)/h; %error here
end
...
end
Change the lines to
om(i,1)=-u(i,2)/h;
om(i,N)=u(i,N-1)/h; % changed colon to comma
That works. Is it doing what you want? I don't know. But there is not an error now.

更多回答（1 个）

Voss
Voss 2022-2-6
The error I run into first is on this line:
om(i,N)=u(i:N-1)/h;
When i == 2, you have
om(2,11) = u(2:10)/0.1;
Just like the error message says, the left-hand side is a single scalar element and the right-hand side is a 1-by-9 vector. How to resolve that depends on what your intent is there, which I don't know.
Note that if that problem were resolved, then you'll have the same type of error on the next iteration with the previous line:
om(i,1)=-u(i:2)/h;
When i == 3, this is
om(3,1)=-u(3:2)/h;
because u(3:2) is empty and om(3,1) is a scalar.
Are these colon operations really supposed to be comma-separated lists (i.e., row/column indexing operations)? That is, u(i,N-1) and u(i,2)? Let me see if that runs:
M=44;
N=11;
N1=6;
h=0.1;
Re=100;
for i=1:M
for j=1:N
u(i,j)=0;
v(i,j)=0;
si(i,j)=0;
om(i,j)=0;
end
end
for j=1:N1
y=(j-1)*h;
u(1,j)=-1.5+6*y*y;
si(1,j)=-0.5-1.5*y+2*y*y*y;
om(1,j)=-12*y;
end
for j=N1+1:N
y=(j-1)*h;
u(1,j)=-18*y*y+12*y-1.5;
si(1,j)=-6*y*y*y+6*y*y-1.5*y-0.5;
om(1,j)=36*y-12;
end
for i=(2:M-1)
si(i,N)=-0.5;
end
for j=(1:N)
y=(j-1)*h;
si(M,j)=-0.25+y*y*y-0.75*y;
u(M,j)=-0.75+3*y*y;
om(M,j)=-6*y;
end
for ite=(1:500)
for i=(2:M-1)
om(i,1)=-u(i,2)/h;
om(i,N)=u(i,N-1)/h;
end
for i=(2:M-1)
for j=(2:N-1)
si(i,j)=(si(i-1,j)+si(i+1,j)+si(i,j-1)+si(i,j+1)+om(i,j)*h*h)/4;
end
end
for i=(2:M-1)
for j=(2:N-1)
omx=(om(i+1,j)-om(i-1,j))/(2*h); %this line seems to be having an issue.
omy=(om(i,j+1)-om(i,j-1))/(2*h);
con=u(i,j)*omx+v(i,j)*omy;
om(i,j)=(((om(i-1,j)+om(i+1,j)+om(i,j-1)+om(i,j+1))-Re*con*h*h)/4);
end
end
end
for i=(1:M)
for j=(1:N)
u1(i,j)=1.5-6*y*y+u(i,j);
v1(i,j)=v(i,j);
end
end
Runs without error.

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