Coding Conventions

Subroutines Arguments

Subroutines arguments should be arranged in the order:

mandatory [in] (input only) arguments, followed by
mandatory [inout] (input and output) arguments, followed by
mandatory [out] (output) arguments, followed by
optional  [in] (input only) arguments, followed by
optional  [inout] (input and output) arguments, followed by
optional  [out] (output) arguments

These should them be declared in separate blocks and commented as follows

subroutine test(arg1, arg2, arg3, arg4, arg5, arg6)
implicit none
! Mandatory input arguments
integer(i4b) , intent(in) :: arg1 !! description of arg1
! Mandatory input/output arguments
integer(i4b) , intent(inout) :: arg2 !! description of arg2
! Mandatory output arguments
integer(i4b) , intent(out) :: arg3 !! description of arg3
! Optional input arguments
integer(i4b) , intent(in) :: arg4 !! description of arg4
! Optional input/output arguments
integer(i4b) , intent(inout) :: arg5 !! description of arg5
! Optional output arguments
integer(i4b) , intent(out) :: arg6 !! description of arg6

Nore that we use !! on the variable description so that is it picked up by F90DOC