Passing different set of variables in a FORTRAN subroutine - fortran

Question

I want to apply three different methods, selected with the value of an integer switch. The first method uses two integers, the second a real array and an integer and the third a real 2D array. In my current implementation, I allocate and pass as parameters all the above data (2 int + real_array + int + real_2array). I could also use a module, but it would be similar. I'm searching for a method to define only the data that my method will use (i.e. only the matrix for method 3) and nothing else. Any suggestions?
Edit:
I have made a simplified version of what I described above.
A part of the main program:
INTEGER :: m, imeth
REAL*8 :: x, y
REAL*8, DIMENSION(:), ALLOCATABLE :: uu, wc
REAL*8, DIMENSION(:,:), ALLOCATABLE :: BCH
imeth = 0
m = 64
ALLOCATE(uu(m), uu_(m), wc(m))
ALLOCATE(BCH(m,m))
if (imeth .EQ. 0) then
x = 1.0d0
y = 2.0d0
elseif (imeth .EQ. 1) then
!Assign values to wc
else
!Assign values to BCH
endif
call subr(m,x,y,uu,uu_,imeth,BCH,wc)
STOP
END
and a subroutine
SUBROUTINE subr(n,a,b,u,u_,imeth,DCH,ws)
IMPLICIT NONE
INTEGER, INTENT(IN) :: n, imeth
REAL*8, INTENT(IN) :: u(n), DCH(n,n), ws(n)
REAL*8, INTENT(OUT) :: u_(n)
INTEGER :: i
if (imeth .EQ. 0) then
u_ = -u_ * 0.5d0 / (a+b)
elseif (imeth .EQ. 1) then
u_ = -u / ws
else
u_ = matmul(DCH,u)
endif
RETURN
END SUBROUTINE subr
I want the main program to have a form like
imeth = 0
m = 64
ALLOCATE(uu(m), uu_(m))
if (imeth .EQ. 0) then
a = 1.0d0
b = 2.0d0
elseif (imeth .EQ. 1) then
ALLOCATE(wc(m))
!Assign values to wc
else
ALLOCATE(BCH(m,m))
!Assign values to BCH
endif
if (imeth .EQ. 0) then
call subrA(m,x,y,uu,uu_)
elseif (imeth .EQ. 1) then
call subrB(m,wc,uu,uu_)
else
call subrC(m,BCH,uu,uu_)
endif

Answer 1

EDIT: After OP added the code I think that using optional arguments in conjunction with the present intrinsic might be better suited for this task. The subroutine could then read
SUBROUTINE subr(n,u_,a,b,u,DCH,ws)
IMPLICIT NONE
INTEGER, INTENT(IN) :: n
REAL*8, INTENT(OUT) :: u_(n)
REAL*8, INTENT(IN),OPTIONAL :: a(n)
REAL*8, INTENT(IN),OPTIONAL :: b(n)
REAL*8, INTENT(IN),OPTIONAL :: u(n)
REAL*8, INTENT(IN),OPTIONAL :: DCH(n,n)
REAL*8, INTENT(IN),OPTIONAL :: ws(n)
INTEGER :: i
if ( present(a) .and. present(b) ) then
u_ = -u_ * 0.5d0 / (a+b)
elseif ( present(u) .and. present(ws) ) then
u_ = -u / ws
elseif ( present(wch) .and. present(u) ) then
u_ = matmul(DCH,u)
else
stop 'invalid combination'
endif
END SUBROUTINE subr
Here is the old answer as it still might be helpful:
Maybe you could try interfaces:
module interface_test
implicit none
interface method
module procedure method1
module procedure method2
module procedure method3
end interface
contains
subroutine method1(int1, int2)
implicit none
integer,intent(in) :: int1
integer,intent(out) :: int2
int2 = 2*int1
end subroutine
subroutine method2(int, realArray)
implicit none
integer,intent(in) :: int
real,intent(out) :: realArray(:)
realArray = real(2*int)
end subroutine
subroutine method3(realArray)
implicit none
real,intent(inout) :: realArray(:,:)
realArray = 2*realArray
end subroutine
end module
program test
use interface_test, only: method
implicit none
integer :: int1, int2
real :: arr1D(10)
real :: arr2D(10,10)
int1 = 1
call method(int1, int2)
print *, int2
call method(int1,arr1D)
print *, arr1D(1)
arr2D = 1.
call method(arr2D)
print *, arr2D(1,1)
end program