While loop data saved into a vector

Hello! I'm trying to solve a sparse linear system A*x=b (A=[],b[],x=[]) and I've got a while loop with all the intermediate steps to find the solution. What I'm trying to do is to save in a vector all the intermediate steps.

        if true
          % code
        end

      xnew=x0;
      k=0;
      counter=0;
      xdata=[];
      maximum number of iterations 2000
      while max(abs(xnew-x))>tol && k <2000,
          k=k+1;
          x=xnew;
          xnew=B*x+c; 
          xdata(counter)=xnew;
          counter=counter+1;
      end
      display(xdata)
      x=xnew;

But I get an error message: "Subscript indices must either be real positive integers or logicals." (About the line that says" xdata(counter)=xnew;

Any ideas?

Thanks in advance!

Answer 1

[Ilham Hardy]

counter = 0;

is the problem..

[Ilham Hardy]

-snip-

.. I get another error -.- In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in jacvec (line 33) xdata(counter)=xnew;

-snip-

Try this

xnew=x0;
      k=0;
      %counter=0;
      xdata=[];
      maximum number of iterations 2000
      while max(abs(xnew-x))>tol && k <2000,
          k=k+1;
          x=xnew;
          xnew=B*x+c; 
          %xdata(counter)=xnew;
          xdata = [xdata xnew];

          %counter=counter+1;
        end
        display(xdata)
        x=xnew;

Answer 2

[Adam]

You initialise counter to 0. 0 is not a real positive integer (or logical). So you should initialise

counter = 1;

and that should be fine. Matlab indexes arrays from 1. I don't know if you are more familiar with languages like C++ where indexing is from 0, but for Matlab this is not the case.

Answer 3

[turtlish]

Thank you both! I changed it but now I get another error -.- In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in jacvec (line 33) xdata(counter)=xnew;