The dimension of my vector changes after a few iterations, how am I writing things incorrectly?

Hello,

Essentially, I am solving a system of linear equations, where Ax=b and A is a numerical scheme, x is a vector in the next time step, and b is the vector that used from the previous time step. I have n points in time, and m points in space (m=total number of points-1)

A doesn't change with each calculation, but it is a mxm matrix My first B is a m by 1 vector with all the points equal 300^1000 My first w is solved by A\b

So I wrote a few loops to now use w from iteration 1 as a B for iteration 2, and then get a w of iteration 2, and so on and so forth. The problem is 1) my matrix randomly grows from 99x1 to 100x1 in a few iterations

2) I am not getting an answer, so I am calculating my B incorrectly

So here's the code. q is used to save a vector after a certain number of iterations as a .csv file to be plotted later

q=0;
WOUT=zeros(m,1);% counter to enite data to csv file
for j=2:n-1,
  q=q+1;   
  for p=2:m-1,
% this says take the w of the previous itr, multiply the %coefficients to in the previous, current, and future point in %space to eventually build a vector B. This vector should be used %to solve w for the next iteration
      BB(j)=(c4.*w(p-1))+(c5(p).*w(p))-(c6.*w(p+1));
      size(BB)
      BB;
      xp=x';  

    end
    w=AA\BB;

    %%loop to output every 10th solution in time

    if q==10 %change this to any number
        w1=w./1000; %convert to L 
        WOUT=[WOUT,w1];
         q=0;
    end
end
toc
csvwrite('k',WOUT)

end

Any additional suggestions and input is welcomed. Everyone here has been great about answering my questions. Thank you!

Answer 1

[Jan]

I neither find "A" nor "B". Do you mean "AA" and "BB"?

What do you expect this line to do: BB;?

xp is calculated, but never used. There is even no x except for this line xp=x';.

Does your question mean, that BB grows from [99x1] to [100x1]? If so, j must be 100, what would be a consequence of n beeing 101 or larger.