precision.f90

! module to define precision of real variables
module prec
  implicit none
  integer, parameter :: dp = selected_real_kind(P=10,R=30)
  integer, parameter :: sp = selected_real_kind(P=5,R=15)
  integer, parameter :: dp_alt = kind(0.d0)

  public :: dp,sp,print_kind_info
  private

 contains
  ! routine to print information about the kinds being used 
 subroutine print_kind_info()
  real(sp) :: pi_single
  real(dp) :: pi_double
 
  print*,'double precision is kind=',dp
  print*,'single precision is kind=',sp
  print*,'kind of a double precision number is ',dp_alt
 
  pi_single = 4.0_sp*atan(1.0_sp)
  pi_double = 4.0_dp*atan(1.0_dp)
  print*,' pi in single precision is ',pi_single
  print*,' pi in double precision is',pi_double

  ! see what happens if we accidently mix precisions
  pi_double = pi_single
  print*, 'pi converted from single is =',pi_double

 end subroutine print_kind_info
end module prec