MATLAB: Trying to make a “snake” matrix

loopsmatrix arraymatrix manipulation

N=5;
M=9;
T=zeros(N,M);
count=0;
for i=1:N
    for j=1:M
        count=count+1;
        T(i,j)=count;
        if mod(i,2)==0
            T(i,j)=fliplr(T(i,j));
        end 
    end
end
T

I'm trying to get the even rows to go 1,2,3,4 and so on to the last column, and then on the even rows I want the elements to flip from left to right. SO far I've got a matrix that goes from 1 to the last element, and I can't seem to get the even rows to flip. Thanks!

Best Answer

N = 5; M = 9;
T = reshape(1:M*N, [M, N])';
T(2:2:end,:) = fliplr(T(2:2:end,:));

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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: Struggling with array dot operator

Define the t-data before the for loop

    T=0:0.1:20;
    for i =1:length(T),
     t=T(i);
  L(:,:,i) = D*diag([(t.^2+1).*(t.^2+1).*(sin(t).^2) (t.^2+1).*(t.^2+1).*
(sin(2*t).^2) (t.^2+1).*(t.^2+1).*(sin(3*t).^2) (t.^2+1).*(t.^2+1).*(sin(4*t).^2) 
(t.^2+1).*(t.^2+1).*(sin(5*t).^2)])*D';
end

Also, it is a good ideas to use commas to explictly separate entries of a vector/matrix.

Best Answer

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MATLAB: Struggling with array dot operator

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