for k=1:n-1
  if(A(k,k) == 0)
    error('Elemento nulo na diagonal');
  end
  for i=k+1:n
    A(i,k) = A(i,k)/A(k,k);
    for j=k+1:n	    
      A(i,j) = A(i,j) - A(i,k)*A(k,j);
    end
  end
end