Guide for good coding

How to create a new module/subroutine

Subroutines should be integrated inside a module. A good writing habit is to add the line "IMPLICIT NONE", in the beginning of the module and subroutine.

First you can define all the variable that belongs to the module and could be used at another place. A good thing is also to create a subroutine that allocate and initialise module variables. If the variable is only modified inside the module it should be taged as protected. If the variable belongs only to the module it can be specified to be private.

You can now start the definition of the subroutine. Start by variable and function from other module if necessary. Comment the purpose of the subroutine directly. Declare the variables, first the one pass in arguments. Use the intent to specify the status of the variable inside the subroutine. Continue with the local and saved variables. Then you can define local variables. Remember to comment all of them, you can specify the dimension if the variable is an allocatable variable as well as the units and everything that seems appropriate.

You can finally write the code.

  1       MODULE aquarium_mod
  2 
  3       IMPLICIT NONE
  4 
  5       INTEGER :: water     ! Define what is the variable, the dimension, units etc..
  6       REAL,SAVE,ALLOCATABLE,DIMENSION(:) :: kre1      ! Another comment (°)
  7 
  8       CONTAINS
  9 
 10 c===== subroutine 1
 11 
 12       SUBROUTINE ini_aquarium(ngrid)
 13 c=======================================================================
 14 c   subject:
 15 c   --------
 16 c   Initialise module s variable
 17 c
 18 c   author: Someone  
 19 c=======================================================================
 20       IMPLICIT NONE
 21       INTEGER, INTENT(IN) :: ngrid
 22 
 23       allocate(kre1(ngrid+1))
 24 
 25       END SUBROUTINE ini_aquarium
 26 
 27 c===== subroutine 2
 28 
 29       SUBROUTINE end_aquarium
 30 c=======================================================================
 31 c   subject:
 32 c   --------
 33 c   Deallocate module s variable
 34 c
 35 c   author: Someone  
 36 c=======================================================================
 37 
 38       IMPLICIT NONE
 39 
 40       IF (allocated(kre1)) deallocate(kre1)
 41 
 42       END SUBROUTINE end_aquarium
 43 
 44 c===== subroutine 3
 45 
 46       SUBROUTINE aquarium(kre, grass, other_things
 47      &   really_anything)
 48                                                          
 49       use another_module_mod, only: fct, variable
 50       
 51 c=======================================================================
 52 c   subject:
 53 c   --------
 54 c   What is the subroutine doing
 55 c
 56 c   author: Someone smart 
 57 c   ------
 58 c   update: Someone smarter, march 2012:
 59 c         - I change something here
 60 c   
 61 c=======================================================================
 62       
 63        IMPLICIT NONE
 64 
 65 c-----------------------------------------------------------------------
 66 c
 67 c    Declarations :
 68 c    --------------
 69 c
 70 c    Input/Output
 71 c    ------------
 72 
 73       REAL, INTENT(IN)    ::  something(ngrid,nlayer) ! 2D tabular used as an input only  (W/m^2)
 74       REAL, INTENT(OUT)   ::  kre(ngrid)              ! 1D tabular output by the subroutine  
 75       REAL, INTENT(INOUT) ::  grass(ngrid,nlayer)     ! Variable that is modified by the subroutine
 76                                                       ! it is an input and output
 77       LOGICAL,INTENT(IN)  ::  really_anything         ! Boolean variable  
 78 
 79 c    Local saved variables :
 80 c    -----------------
 81       INTEGER, PARAMETER :: nb_kre = 6                ! Number of kre
 82       INTEGER, SAVE      :: rock                      ! Another variable
 83       LOGICAL,SAVE :: firstcall=.true.                ! Another variable
 84 
 85 c    Local variables :
 86 c    -----------------
 87       REAL tabular(ngrid)                             ! Local var
 88       INTEGER i                                       ! Loop var
 89 
 90 c    Beginning of the code :
 91 c    ----------------- 
 92 
 93       IF (firstcall) THEN
 94         ! identify where are the kre
 95         DO i=1,nb_kre
 96           kre(i)=i
 97           write(*,*) "the Kre ", i, "is behind the rock"
 98         ENDDO !end of the loop nb_kre
 99       ENDIF   !end firstcall
100 
101       END SUBROUTINE aeropacity
102       
103       END MODULE aeropacity_mod