%Compute the exact value of exp(-5)
function y = exp_exa(n)
 
  if (mod(n,2) == 0)
    s1 = 1;
    s2 = 0;
    for i = 1:n/2
      s1 = s1 + 5^(2*i) / factorial(2*i);
      s2 = s2 + 5^(2*i-1) / factorial(2*i-1);
      y = s1 - s2;
    end
  else
    s1 = 0;
    s2 = 0;
    for i = 0:(n-1)/2
      s1 = s1 + 5^(2*i) / factorial(2*i);
      s2 = s2 + 5^(2*i+1) / factorial(2*i+1);
      y = s1 - s2;
    end
  end
  
end

%Result: n = 33:45, exp_exa = 0.006737946999 095