Do the following two questions:

1. Write a Fortran 90 FUNCTION which computes N factorial (i.e. N!). Input: a positive integer N. Returns: N Factorial.

Solution:

FUNCTION Factorial(N)

IMPLICIT NONE

INTEGER :: Factorial, I

INTEGER, INTENT(IN) :: N

DO I=1, N

Factorial=Factorial*I

END DO

END FUNCTION Factorial

2. Write a Fortran 90 SUBROUTINE which computes the sum of the integers greater than or equal to 1 and less than or equal to N. Input: a positive integer N. Returns: the sum of the integers greater than or equal to 1 and less than or equal to N.

Solution:

SUBROUTINE Sum_Sub(N, MySum)

IMPLICIT NONE

INTEGER, INTENT(IN) :: N

INTEGER, INTENT(OUT) :: MySum

INTEGER :: I

MySum=0

DO I=1, N

MySum=MySum+I

END DO

END SUBROUTINE Sum_Sub