solve a system of lineare equation gauss Jordan method in matlab

Question

I try to solve system of lineare equation using the Gauss Jordan methode. I try my code with a smaller matrice and I got the rigth answer. Now I try it with a bigger matrice and I got NAN(not a number) as answer. I don't what I am doing wrong.

    a = [-1 0 0 0 0 0 1 0 0 0 1 0 0 0;
0 -1 0 0 0 0 0 1 0 0 0 1 0 0 ;
1 0 -1 0 -1 0 0 0 0 0 0 0 0 0;
0 1 0 -1 0 -1 0 0 0 0 0 0 0 0;
0 0 0 0 1 0 0 0 0 0 -1 0 -1 0;
0 0 0 0 0 1 0 0 0 0 0 -1 0 -1;
0 0 1 0 0 0 -1 0 -1 0 0 0 0 0;
0 0 0 1 0 0 0 -1 0 -1 0 0 0 0;
-0.025 0 1 0 0 0 0 0 0 0 0 0 0 0;
0 -0.8 0 1 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 -0.04 0 0 0 0 0 1 0 0 0;
0 0 0 0 0 -0.96 0 0 0 0 0 1 0 0;
0 0 -0.04 0 0 0 0 0 1 0 0 0 0 0;
0 0 0 -0.96 0 0 0 0 0 1 0 0 0 0];

    b = [-50;-50;0;0;0;0;0;0;0;0;0;0;0;0];
    Gaussjordan(a,b);
    % Function  Gauss Jordan
   function x=Gaussjordan(a,b)
     ab=[a b]; 
     [m,n]=size(ab); %size of matrix
       for i=1:m
         ab(i,:)=ab(i,:)/ab(i,i);
          for j=1:m
            if j==i; continue;
          end
         ab(j,:)=ab(j,:)-ab(j,i)*ab(i,:);
       end;
     end;
   x=ab(:,length(b)+1);
   end

with the samll matrix a = [1 1 1; 2 -3 4; 3 4 5] b = [9; 13; 40], I got the answer ans = [1 3 5].

But with the bigger one upon in code I got ans = [NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN]

Did someone has an idea? Ps: I solve this systen of equation with fsolve to be sure that it exist an answer on the system equation