Using Fortran90's intrinsic random number generator, using either a specified seed or using the system clock

random_number_demo.f90

!
! Program to demonstrate the use of Fortran 90's intrinsic random_number() 
!
program main

	integer :: values(8), k, nseed
	integer, dimension(:), allocatable :: seed

	real(8) :: r(10)

	!
	! Step 1: To over-ride "default seed", you have to initialize it first
	!

	call random_seed(size = k)
	allocate(seed(1:k))

	!
	! Step 2a: You may use the "milliseconds" from the system clock to set it automatically
	!

	call date_and_time(values=values)  ! t

	seed(:) = values(8)

	!
	! Step 2b: Or set it to a value you want (to reproduce errors for example)
	! UNCOMMENT TO USE
	!

	! nseed = 5
	! seed(:) = nseed
	! call random_seed(put = seed)

	!
	! A call to random_number populates the "matrix" "r" in general
	!
	call random_number(r)
	
	do i = 1, 10
                write(*,'(f7.4)') r(i)
	enddo
		
end program main