The missing factorial function

[urbanjost]

Why does Fortran not have a factorial function?

It does, as for positive whole values of X the Gamma function simplifies to the factorial function for (X-1). That is,

x! == gamma(x+1)

program testit
use, intrinsic :: iso_fortran_env, only : wp=>real64
integer,parameter :: n(*)=[0,1,5,11,170]
integer :: j

   do j=1,size(n)
      write(*,'(*(g0,1x))')'factorial of', n(j),' is ', &
       & product([(real(i,kind=wp),i=1,n(j))]),         &
       & ' or ',                                        &
       & gamma(real(n(j)+1,kind=wp))
   enddo

end program testit

[Beliavsky]

Posted, thanks!