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Selection of the KIND values for real and integer variables

 
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jayxwang



Joined: 13 Jun 2011
Posts: 3
PostPosted: Thu Jun 23, 2011 4:06 am    Post subject: Selection of the KIND values for real and integer variables Reply with quote
In a fortran-77 written program, the real variables are defined as: Implicit double precision (A-H, O-Z).

When the program was compiled using FTN-95, link errors come up with the values of KIND for some arrays seemingly different in differnt subroutines. I am wondering if the real variable must be defined in each subroutine by adding up the the following two lines:

integer, parameter :: dp=kind(1.d0)
real (kind=dp) :: x,y,z....

Values of KIND for those real and integer variables should be the same in the program?

Thanks,
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2554
Location: Sydney
PostPosted: Thu Jun 23, 2011 5:14 am    Post subject: Reply with quote
FTN95 uses different values of KIND to most other compilers, so your use of "dp" is a good idea.
I have listed a program below to give some examples of using double precision and also extended precision.
It demonstrates you must be careful when defining both double and extended precision constants.
My preference is to use the non-standard definition "REAL*8", which is the clearest and most concise definition.
Code:
integer, parameter :: dp = kind (1.d0)
integer, parameter :: qp = selected_real_kind (17)
!
  real (kind=dp) :: x,y,z
  real (qp) :: q,r
  real*8 a
  integer*4 i
!
  a = 0.1d0
  x = 0.1_dp
  y = 0.1d0
  z = 0.1
  q = 0.1_qp
  r = 0.1d0
!
  write (*,*) 'double precision',a,x,y,z
  write (*,*) 'extended precision',q,r
  write (*,*) 'dp =',dp
  write (*,*) 'qp =',qp
!
  do i = 5,20
    write (*,*) i, selected_real_kind (i)
  end do
!
  end
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