Fortran functions: some examples

Transcription

1 Laboratorio di Calcolo di Aerodinamica a.a. 2016/17 DIMA, Sapienza University of Rome, Italy April 4, 2017

2 Definite DO statement fattoriale.f90 code 1!file: fattoriale.f90 2!This program reads a number and compute the factorial 3 PROGRAM fattoriale 4!sezione dichiarativa 5 IMPLICIT NONE 6 INTEGER:: n, m 7 INTEGER:: fact 8!sezione esecutiva 9 WRITE(*,*) Write the number on the screen and press ENTER 10 READ(*,*) n 11 fact=n 12 DO m=1,n-1 13 fact=fact*(n-m) 14 ENDDO 15 if (n.eq.0) fact=1 16 WRITE(*,*) The factorial of, n, is:,fact 17!sezione esecutiva 18 STOP 19 END PROGRAM fattoriale

3 Undefinite DO statement: mcd.f90 code 1!file: mcd.f90 2!This program prints the greater common divisor of two integers 3 PROGRAM mcd 4!sezione dichiatativa 5 IMPLICIT NONE 6 INTEGER:: a, b, m 7!sezione esecutiva 8 WRITE(*,*) Insert two number separated by a space: 9 READ(*,*) a, b m=a 12 IF (b.lt.a) m=b 13 DO 14 IF (mod(b,m).eq.0.and.mod(a,m).eq.0) EXIT 15 m = m-1 16 ENDDO 17 WRITE(*,*) The greater common divisor is,m 18!sezione conclusiva 19 STOP 20 END

4 Modules: subprograms modules are useful for engineering applications they are useful for public use the module is a black box: - it is important WHAT it does - it is not important HOW the subprograms are useful in two cases: - to do more than once the same instructions - for parametric instructions

5 Sub-programming pro it is useful to avoid semantic errors: ordered and precise structure the subprogram can be used in other contexts two types of subprograms will be used: - SUBROUTINE - FUNCTION they can be written in different files.f90 : COMPILATION and LINKING is mandatory they can be written in the same file of the main program: COMPILATION and LINKING are simultaneous actions

6 Subprograms each subprogram is called in the main program (or in other subprograms) two variable are defined - dummy variable: useful for communications between the calling program and the subprogram, NO MEMORY IS USED - local variable: used in the subprograms and deallocated at its the end, THE MEMORY IS TEMPORARILY OCCUPIED! in the main program... CALL nome_subroutine(arguments)...!the subroutine program SUBROUTINE nome_subroutine(arguments) IMPLICIT NONE RETURN END

7 Subroutine use: massimo.f90 code 1! File: massimo.f90 2! Calcolo del massimo dati due numeri 3 PROGRAM massimo 4! Sezione dichiarativa 5 IMPLICIT NONE 6 INTEGER :: num1, num2, mas 7! Sezione esecutiva 8 WRITE(*,*) Inserisci due interi (separati da spazio) 9 READ(*,*) num1, num2 10 call calc(num1,num2,mas) 11 WRITE(*,*) Il massimo e :,mas 12! Sezione conclusiva 13 STOP 14 END PROGRAM massimo 15! 16! 17 SUBROUTINE calc(x,y,z) 18 IMPLICIT NONE 19 INTEGER:: x,y,z 20 IF (x.gt.y) then 21 z = x 22 ELSE 23 z = y 24 ENDIF 25 RETURN 26 END SUBROUTINE calc

8 subroutine & function arguments have to be declared both in the main program and in the subroutine no STOP at the end but RETURN same rules as the main program Some differences are in the FUNCTION case: the function is a variable itself the type of this variable (i.e. of the function) has to be declared the function is used as a variable in expressions in the calling the keyword CALL is not used the function returns only one value at time, in the other cases the subroutine subprogram has to be used

9 Function use: massimo.f90 code 1! File: massimo.f90 2! Calcolo del massimo dati due numeri 3 PROGRAM massimo 4! Sezione dichiarativa 5 IMPLICIT NONE 6 INTEGER :: num1, num2, mas, calc 7! Sezione esecutiva 8 WRITE(*,*) Inserisci due interi (separati da spazio) 9 READ(*,*) num1, num2 10 mas = calc(num1,num2) 11 WRITE(*,*) Il massimo e :,mas 12! Sezione conclusiva 13 STOP 14 END PROGRAM massimo 15! 16! 17 FUNCTION calc(x,y) 18 IMPLICIT NONE 19 INTEGER:: x,y,calc 20 IF (x.gt.y) then 21 calc = x 22 ELSE 23 calc = y 24 ENDIF 25 RETURN 26 END FUNCTION calc