MATLAB: Where is the wrong in this equations between for loop

sor successive over relaxation method;

clear
clc
w=1.8;
n=111;
m=33;
hx= 4/32 ;                                      %space betweem nodes in x direction
hy=20/110+1;    
h=hy/hx;
E0=8.85*10^(-12);    
v_now= zeros(n,34);
d=2:33;
v_now(110,d)=100;
v_now(105,14:21)=100;
v_prev= zeros(n,34);
v_now(:,34)=v_now(:,2);
iter=0;
[x y]=ndgrid(1:111,1:32);
error=(sum(sum((abs(v_now-v_prev))/m*n)));
while(error>0.01)%Run this until convergence
    [x,y]= meshgrid(1:34,1:111)
      iter=iter+1; % Iteration counter increment
*for i=105
                for j=2:12
                        E (i, j)= 8.85*10.^(-12);
                        E (i-1,j)=8.85*10.^(-12);
                        E (i-1, j-1)=8.85*10.^(-11);                %%permittivity of interface region
                        E (i, j-1)=8.85*10.^(-11);
                          a=(E (i, j)+E (i, j-1));
                          b=(E (i-1,j)+E (i-1, j-1));
                          c= E (i, j)+E (i-1, j);
                          d=E (i, j-1)+E (i-1, j-1);
                          W1 (i, j)=(h.^2).*a;
                          W2 (i, j)=(h.^2).*b;
                          W3 (i, j)=c;
                          W4 (i, j)=d;
                          W (i, j)=a+b+c+d;
                           v_now (i, j)= (1-w).*(v_prev (i, j))-w*(W1 (i, j).*(v_prev (i+1, j))+W2 (i, j).*(v_now (i-1, j))+W3 (i, j).*(v_prev (i, j+1))+W4 (i, j).*(v_now (i, j-1)))/(W (i, j));
                               end
                               end*__******
  *
  [x y]=ndgrid(1:111,1:34);
  error=(sum(sum((abs(v_now-v_prev))/m*n)));
     v_prev=v_now; % Updating previous iteration matrix to the last iteration performed
    surf(x,y,v_now)
    set(gca)
    title('potential ')
    xlabel('i')
    ylabel('j')
    zlabel('v_now')
  end

Best Answer

Your loop doesn't seem to change anything. You only use i and j for indexing, and all your values for E will be 8.85*10.^(-12) or 8.85*10.^(-11). Therefore, your value of v_now won't change.

Related Solutions

MATLAB: MATLAB code never stops running (infinite loop)

Around line 62 or so you have

for n=1:now

Within that for loop, around line 140 or so you have

                 if m ==1
                    for j = 1:nos
                        for n = 1:now
                            for i=1:noc
                                Permf(n,i)=P(j,i);
                            end
                        end
                    end
                end

Notice that you have the for n inside the for n . MATLAB does define what happens when you do this: the change to n will be in effect until the next outer for n starts, at which point n will be set to the "next" value of the outer loop as-if the change to n had not been done. But meanwhile until the bottom of the loop, n has changed. In particular at your line just inside the inner while loop you are having problems with,

                     functiontemp=Ftotal(n,m);

the n that is going to be used there is the n that was left-over from the inner for n loop, not the n associated with the outer for n loop.

Notice as well that the assignment to Permf is inside a triple for loop but is assigning to a variable using only two indices. The value that Permf(n,i) is going to be left with is going to be the last value assigned to it. You could achieve the same effect with

Permf(1:now, 1:noc) = P(nos, 1:noc)

and since you are not initializing Permf (growing it inside the loop) and it is always the same size, this in turn could be expressed as

Permf = repmat(P(nos, :), now, 1);

with no loop.

Are you sure that is what you want Permf to be assigned?

Any time you have a for loop that is not doing reduction (e.g., totaling the P values) and has more nesting levels than the number of indices of the output variable, then you should be optimizing to do only what would be left in the final result after the overly-nested assignments were complete.

MATLAB: How to give different colors to different tracts

By sugestion of the cyclist:

I found it. If anyone needs it there it is:

function []= Test (TRACTS%%Cell with structs within, INFO%Information about each tract)

   close all; 
   for i=1:INFO.n_count 
       clear V; 
       for j=1:size(TRACTS{i}) 
       G(j) = TRACTS{i}(j,1); %Info about x axis 
       H(j) = TRACTS{i}(j,2); %Info about y axis
       I(j) = TRACTS{i}(j,3); %Info about z axis    
       J = G(j)-G(1); 
       K = H(j)-H(1); 
       L = I(j)-I(1); 
       V(j,1)=J; 
       V(j,2)=K;
       V(j,3)=L;       
       W(i,j) = abs(V(j,1))+abs(V(j,2))+abs(V(j,3));       
       end   
       %knowing that RGB color codes are [a b c]
       %we consider the weight that each V has in the W
       %obtaining something like [0.1 0.2 0.6]
       M = [abs(V(j,1))/W(i,j) abs(V(j,2))/W(i,j) abs(V(j,3))/W(i,j)];
      plot3(TRACTS{i}(:,1),TRACTS{i}(:,2),TRACTS{i}(:,3),'Color',M);grid on;
   hold on;
   end
end

I am not sure of what you pretended Jan Simon. I need to change the number of iterations for each position of the cell TRACTS, because the number of points used to generate a track differs. I made this code and he works reasonibly well. However i am open to any changes that you or anyone sugest in order to enhance this code :)

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