MATLAB: Is the code not implementing for i==6 value

error

T = zeros(7,12);
for i = 1:7
  for j = 1:12
    if (i==1 || i==7)
      T(i,j) = 1750;
    end
    if i==4 && (j>3 && j<9)
      T(i,j) = 600;
    end
    if (i==2 || i==6) && (j>1 && j<11)
      T(i,j) = (T(i+1,j)+T(i,j+1)+T(i-1,j)+T(i,j-1))/4;
    end
  end
end

Any help would be appreciated.

Best Answer

I see one apparent error. The condition (i==1 i==7) will never be true. You need an 'or' symbol in it: (i==1 | i==7).

Also notice that when i is equal to 6, T(i+1),j) will not have been set to 1750 as yet, so the expression

   T(i,j) = (T(i+1,j)+T(i,j+1)+T(i-1,j)+T(i,j-1))/4;

may not give you the value you expect. To correct this will require rewriting the routine. Set up your 1750's and 600's first, then do the computation for i==2 | i==6.

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MATLAB: MATLAB question regarding loop

Lots wrong with that code. Gladd to see that you're using a failsafe (limit to number of iterations though). Here, just try this. I fixed several things.

FL=0.04;        %Fin length
BL=0.005;       %Base length
TL=BL+FL;       %Total length
FW=0.010;       %Fin width
BW=0.030;       %Base width
dx=0.001;
dy=dx;
%Total Nodes
M=round(((BW/2)/dx+1));  % i Direction
N=round(((TL)/dx+1));    % j Direction
%Initial Temperature
T=zeros(M,N);
maxLoopIterations = 10000;              % Number of Iterations
err_max = 1e-6;   % Maximum Error
n=0; %Number of Iterations
err = zeros(1, maxLoopIterations);
while n < maxLoopIterations
  n=n+1;
  Tp=T;
  for i=1:1:M
    for j=1:1:N
      %Corner Node 8
      if i==1 && j==1 %(i=0, j=0)
        T(i,j)=(1/2)*(T(i,j+1)+T(i+1,j))+(7500/89)*dx;
        
        %Corner Node 13
      elseif i==M && j==1 %(i=15, j=0)
        T(i,j)=(1/2)*(T(i,j+1)+T(i-1,j))+(7500/89)*dx;
        
        %Corner Node 9
      elseif i==1 && j==N %(i=0, j=45)
        T(i,j)= (89*(T(i+1,j)+T(i,j-1))+4500*dx)/(150*dx+178);
        
        %Constant heat flux boundary node 5
      elseif i>1 && i<M && j==1 %(i=1 to 14, j=0)
        T(i,j)=(1/4)*(T(i-1,j)+T(i+1,j))+(1/2)*(T(i,j+1))+(7500/89)*dx;
        
        %Symmetrical boundary node 2
      elseif i==1 && j>1 && j<N %(i=1 , j=1 to 45)
        T(i,j)=(1/4)*(T(i,j+1)+T(i,j-1))+(1/2)*(T(i+1,j));
        
        %Convective boundary node 7
      elseif i>1 && i<6 && j==N  %(i=1 to 4 , j= 45)
        T(i,j)=((89)*(T(i-1,j)+T(i+1,j))+(178)*(T(i,j-1))+9000*dx)/(300*dx+356);
        
        %Convective Corner Node 10
      elseif i==6 && j==N  %(i=5 , j= 45)
        T(i,j)=((89)*(T(i-1,j)+T(i,j-1))+9000*dx)/(300*dx+178);
        
        %Convective Boundary Node 3
      elseif i==6 && j>5 && j<N  %(i=5, j= 5 to 44)
        T(i,j)=((89)*(T(i,j+1)+T(i,j-1))+178*T(i-1,j)+9000*dx)/(9000*dy+356);
        
        %Corner Node 11
      elseif i==6 && j==6   %(i=5, j=5)
        T(i,j)=((178)*(T(i-1,j)+T(i,j-1)+T(i+1,j)+T(i,j+1))+4500*dy)/(150*dy+534);
        
        %Corner Node 12
      elseif i==M && j==6   %(i=15, j=5)
        T(i,j)=((89)*(T(i-1,j)+T(i,j-1))+4500*dx)/(150*dx+178);
        
        %Convective Boundary Node 6
      elseif i>5 && i<M && j==6   %(i=5 to 15, j=5)
        T(i,j)=((178)*(T(i,j-1))+(89)*(T(i+1,j)+T(i-1,j))+9000*dx)/(9000*dx+356);
        
        %Symmetrical Boundary Node 4
      elseif i==M && j>1 &&j<6   %(i=15, j=1 to 4)
        T(i,j)=(1/4)*(T(i,j-1)+T(i,j+1))+(1/2)*(T(i-1,j));
        
        %Internal Node 1 (SOLID)

      elseif i>1 && i<M && j>1 && j<6
        T(i,j)=(1/4)*(T(i,j-1)+T(i,j+1)+T(i+1,j)+T(i-1,j));
        
        %Internal Node 1 (SOLID)
      elseif i>1 && i<6 && j>5 && j<N
        T(i,j)=(1/4)*(T(i,j-1)+T(i,j+1)+T(i+1,j)+T(i-1,j));
        
      end
    end
  end
  diffMatrix = abs(T - Tp);
  err(n) = max(diffMatrix(:));
  if err(n) < err_max
    break
  end
end
% Crop off unused part of array
err = err(1:n);
plot(err, 'b-', 'LineWidth', 2);
grid on;
drawnow;
fontSize = 20;
title('Error vs. Iteration Number', 'FontSize', fontSize);
xlabel('Iteration Number', 'FontSize', fontSize);
ylabel('Error', 'FontSize', fontSize);
xticks(0:100:n);
yticks(0:.01:.15);

MATLAB: How to make countour plot zoomed out

Hi William Donovan

Simplest way to doing this is by setting the axis limits.

Here i am just mentioning one example.

contour(T)
xlim([-20 20]) % Here -20 to 20 are x axis limit. As i can see you are plotting just 'T' your x data may be just index of data points, so might your limit start from 0 to number of data points.
ylim([-10 10]) % Similar to x also limit the y

Best Answer

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MATLAB: How to make countour plot zoomed out

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