Matlab编码有助于矩阵的manupulation

Question

I am working on this coding for my heat transfer class. The number are suppose to be other equations but I replaced them with numbers to simply it

l=.2;

w=.2;

dx=.05;

dy=.05;

k=400;

q=500;

Nx = (l/dx+1); %nodes in the x direction

Ny = (w/dy+1); %nodes in the y direction

T=zeros(Nx,Ny);

for m = (1:Nx) %node counter in x nodes

   for n = (1:Ny) %node counter in y nodes

      if n==1;  %left side
           T(m,n)=50;

      elseif m==1 && n<Ny;%Heat Flux

           T(m,n)=60;

      elseif m>=2 && n==Ny && m<Nx;  %insulated, right side
           T(m,n)=70;

      elseif n>=2 && n<=Ny-1 && m==Nx ; %insulated, bottom side

           T(m,n)=80;

      elseif m>=((.325*l)/dx)+1 && m<=((.675*l)/dx)+1 && n>=((.325*w)/dy)+1 && n<=
((.675*w)/dy)+1;

           T(m,n) = 400;%center or steam 
      elseif m>1 && m<Nx && n>1 && n<Ny

           T(m,n) = 90;

       elseif m==1 && n==Ny;

           **T(m,n)=T(m+2,n)/2;%**<-------------------this wont work properly**** 

       elseif n==Nx && m==Ny;

           T(m,n)= 110;



      end

   end

end

I am not sure why it will not choose the correct value and divide it by 2 rather it is saying the answer is 0 when it is suppose to be T(2,5) which is 70/2=35?

T =

    50    60    60    60     0
    50    90    90    90    70
    50    90   400    90    70
    50    90    90    90    70
    50    80    80    80   110

any help would be appreciate it

Thanks

Answer 1

As I see it,

You are trying to access the element of the Matrix which is still initialized to zero. T Matrix is Zero(5,5).

And the condition : if m==1 && n==Ny gets executed early in the iteration, at which time, m=1, and n=5 and T(2,5)=0.

So you have T(1,5)=0

So, I would suggest you debug the code and you check the content of Matrix M at the end of each iteration.

Answer 2

The reason T(1,5) is zero is that the indicated line of code is executed at a point when T(3,5) is still set to zero - it has not yet been filled with the value 70, and therefore T(1,5) is set to 0/2 = 0.

If you loop through the values of m in reverse order, by modifying the code to be

for m = (Nx:-1:1)

you'll find that T(3,5) is now set to 70 before T(1,5) is set, and T(1,5) is now correctly set to 35.