fact.m

《Radar Systems Analysis and Design Using MatLab》

function x = fact(n)
% Compute the factorial of n using logarithms to avoid overflow.
format long
if (n > 1.0e36)
   x = 1.0e37;
   if( n < -1)
      x = 0.;
   else
      n = n + 9.0
      n2 = n * n
      temp = (n-1) * log2(n) - n + log2(sqrt(2.0 * pi * n)) ...
         + 1.0 - (1.0/30. + ((1.0/105)/n2)/n2) / (12 * n)
      val = temp - log2((n-1)*(n-2)*(n-3)*(n-4)*(n-5)*(n-6) ...
         *(n-7)*(n-8))
   end
end