Hello World!
program hello
implicit none
print*, 'Hello World!'
end program hello
$ ./a.out
Hello World!
If
- Example - usual
if (i > 0) print *, i
or
if (i > 0) then
r=i*100
else
r=-i*100
endif
print *, r
- Example - Arithmetic
if (expression) Negative, Zero, Positive
program if
implicit none
integer :: i
i = -1
if (i) 10, 20, 30
i = 0
if (i) 10, 20, 30
i = 1
if (i) 10, 20, 30
10 print *, 'i is negative'
20 print *, 'i is zero'
30 print *, 'i is positive'
$ ./.a.out
i is negative
i is zero
i is positive
Select case
if의 순차적인 선택과 다르게 병렬적 선택이며, if문 보다 간결하다.
program select_case
implicit none
integer :: n, k
print *, 'Enter the value ='
read *, n
select case (n)
case (:0)
k = -k
case (10:20)
k = n + 10
case default
k = n
end select
print *, 'k =', k
end program select_case
Goto
유용하게 사용하는 기능 중 하나이다. 단순히 goto 10 처럼 사용할 수도 있고 다음처럼 조건에 따른 사용도 가능하다.
GOTO(label 1, label 2, ..., label n) inter 'n'th-label
program merge
implicit none
integer :: i
read *, i
goto(10, 20, 30, 40) mod(i,4)
10 print *, '1'
goto 50
20 print *, '2'
goto 50
30 print *, '3'
goto 50
40 print *, '4'
print *, 'otherwise'
50 continue
end program merge
$ ./a
3
3
Do loop
program do_loop
implicit none
integer :: i=0, j=0
do
i = i + 1
if(mod(i,2)==0)cycle
if(i > 10)exit
print *, 'i =', i
end do
print *, ''
do while(j <= 10)
j = j + 1
if(mod(j,2)==1)cycle
print *, 'j =', j
end do
end program do_loop
$ ./a.out
i = 1
i = 3
i = 5
i = 7
i = 9
j = 2
j = 4
j = 6
j = 8
j = 10
Array
- Example - static array
고정된 크기를 가지는 행렬이다.
real a, b, c
dimension a(100), b(10,10), c(2,3,4)
or
real, dimension(100) :: a ! 1D
real, dimension(10,10) :: b ! 2D
real, dimension(2,3,4) :: c ! 3D
or
real a(100), b(10,10), c(2,3,4)
or
real a(1:100), b(3:12,2:11), c(1:2,4:6,3:6)
- Example - dynamic array
차원만 정해놓고 크기는 정해놓지 않은 행렬을 말한다.
integer, dimension(:), allocatable :: string ! 1D
program allocate
implicit none
integer, allocatable :: a(:), b(:)
integer :: istat
character(80) :: string='Success'
allocate(a(5), source=1, stat=istat, errmsg=string)
allocate(b,source=a*10)
print *, 'State =', istat, 'ErrMSG = ', trim(string)
print *, a
print *, b
end program allocate
$ ./a.out
State = 0 ErrMSG = Success
1 1 1 1 1
10 10 10 10 10
- Example - pointer array
행렬의 값을 point해서 보여준다.
program pointer
implicit none
integer :: l, i, j, k, m, n
real, target :: b(6,6)=1
real, pointer :: u(:,:), v(:), w(:,:)
print *, b
print *, '---------'
m=3; n=2
i=2; j=4
n=6
do k=1,6
do l=1,6
b(l,k)=2*l+k
end do
end do
print *, b
print *, '---------'
u => b(i:i+2, j:j+2)
print *, u
print *, '---------'
allocate(w(m,n))
w = 9
v => b(:,j)
print *, v
print *, '---------'
v => w(i-1, 1:n:2)
print *, v
end program pointer
아래 결과에서 행렬처럼 적어 두었지만, 사실 결과값은 하나의 열이다.
$ ./a.out
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
1.00000000 1.00000000 1.00000000 1.00000000 1.00000000 1.00000000
---------
3.00000000 5.00000000 7.00000000 9.00000000 11.0000000 13.0000000
4.00000000 6.00000000 8.00000000 10.0000000 12.0000000 14.0000000
5.00000000 7.00000000 9.00000000 11.0000000 13.0000000 15.0000000
6.00000000 8.00000000 10.0000000 12.0000000 14.0000000 16.0000000
7.00000000 9.00000000 11.0000000 13.0000000 15.0000000 17.0000000
8.00000000 10.0000000 12.0000000 14.0000000 16.0000000 18.0000000
---------
8.00000000 10.0000000 12.0000000
9.00000000 11.0000000 13.0000000
10.0000000 12.0000000 14.0000000
---------
6.00000000 8.00000000 10.0000000 12.0000000 14.0000000 16.0000000
---------
9.00000000 9.00000000 9.00000000
- structure
Fortran과 C는 메모리 주소의 구조가 다르다. 주소를 채우는 방식을 알고 있어야 데이터를 다룰 때 올바로 다룰 수 있다. loop문을 다룰 때도 배열의 이해가 요구된다.
| a(0,0) | a(0,1) | a(0,2) |
|---|---|---|
| a(1,0) | a(1,1) | a(1,2) |
| a(2,0) | a(2,1) | a(2,2) |
- Column-major order (Fortran)
do j=0,2
do i=0,2
print *, a(i,j)
end do
end do
| a(0,0) | a(1,0) | a(2,0) | a(0,1) | a(1,1) | a(2,1) | a(0,2) | a(1,2) | a(2,2) |
|---|---|---|---|---|---|---|---|---|
- Column-major order (C)
for(i=0;i<3;i++)
for(i=0;i<3;i++)
print('%d\n', a[i][j]);
| a(0,0) | a(0,1) | a(0,2) | a(1,0) | a(1,1) | a(1,2) | a(2,0) | a(2,1) | a(2,2) |
|---|---|---|---|---|---|---|---|---|
- function
program array_function
implicit none
integer, dimension(-10:10, 23, 14:28) :: a
integer :: d(3)
print *, lbound(a)
print *, lbound(a,1)
print *, ubound(a)
print *, ubound(a,1)
print *, shape(a)
print *, size(a)
print *, size(a,1)
d = shape(a)
print *, d
print *, size(d)
print *, shape(d)
end program array_function
$ ./a.out
-10 1 14
-10
10 23 28
10
21 23 15
7245
21
21 23 15
3
3
- expression
program array_expression
implicit none
integer :: i, j, k
real, dimension(3,3) :: a, c
real, dimension(9) :: b
a = reshape((/(k,k=1,9)/),(/3,3/))
b = (/a + 1.3/)
c = reshape(b,(/3,3/))
print *, a
print *, '-----------'
print *, b
print *, '-----------'
do i=1,3
print *, c(i,:)
end do
print *, '-----------'
b = (/((a(j,k) + 1.3, k=1,3), j=1,3)/)
c = reshape(b,(/3,3/))
print *, b
print *, '-----------'
do i=1,3
print *, c(i,:)
end do
end program array_expression
$ ./a.out
1.00000000 2.00000000 3.00000000 4.00000000 5.00000000 6.00000000 7.00000000 8.00000000 9.00000000
-----------
2.29999995 3.29999995 4.30000019 5.30000019 6.30000019 7.30000019 8.30000019 9.30000019 10.3000002
-----------
2.29999995 5.30000019 8.30000019
3.29999995 6.30000019 9.30000019
4.30000019 7.30000019 10.3000002
-----------
2.29999995 5.30000019 8.30000019 3.29999995 6.30000019 9.30000019 4.30000019 7.30000019 10.3000002
-----------
2.29999995 3.29999995 4.30000019
5.30000019 6.30000019 7.30000019
8.30000019 9.30000019 10.3000002
- reshape
reshape(array_data, shape, pad, order)
- array_data : reshape하고자 하는 array.
- shape : 바꾸려는 shape
- pad : reshape한 array가 더 클경우 비어있는 위치의 채울 값
- order : 정렬하고자 하는 차원 (행이 첫 번째 차원, 열이 두 번째 차원)
program array_reshape
implicit none
integer :: i, j
integer, parameter, dimension(4,4) :: ident4 = reshape((/(1,(0, i=1,4), j=1,3),1/),(/4,4/))
integer, dimension(2,2) :: a = reshape((/1,2,3,4/),(/2,2/)), b
integer :: c(2,3)
do i=1,4
print *, ident4(i,:)
end do
print *, '------------'
do i=1,2
print *, a(i,:)
end do
print *, '------------'
b = reshape(a,(/2,2/),order=(/2,1/))
print *, b(1,:)
print *, b(2,:)
print *, '------------'
c = reshape(a,(/2,3/),pad=(/0/),order=(/2,1/))
print *, c(1,:)
print *, c(2,:)
end program array_reshape
$ ./a.out
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
------------
1 3
2 4
------------
1 2
3 4
------------
1 2 3
4 0 0
- mask
where(mask)에서 mask가 true일 때만 배열 원소 값을 할당.
program array_mask
implicit none
integer :: i, j
integer, dimension(2,2) :: a, b = reshape((/2,4,6,8/),(/2,2/)), &
c = reshape((/2,0,0,2/),(/2,2/))
where(c /= 0)
a = b/c
else where
a = b
end where
print *, b(1,:)
print *, b(2,:)
print *, '------------'
print *, c(1,:)
print *, c(2,:)
print *, '------------'
print *, a(1,:)
print *, a(2,:)
end program array_mask
$ ./a.out
2 6
4 8
------------
2 0
0 2
------------
1 6
4 4
- forall
where(mask)의 확장형이다.
program array_forall
implicit none
integer :: i, j
integer, dimension(3,3) :: a = reshape((/(i, i=1,9)/),(/3,3/))
print *, a(1,:)
print *, a(2,:)
print *, a(3,:)
forall(i=1:3,j=1:3,j>i) a(i,j) = 0
print *, '----------'
print *, a(1,:)
print *, a(2,:)
print *, a(3,:)
end program array_forall
1 4 7
2 5 8
3 6 9
----------
1 0 0
2 5 0
3 6 9
Statement function
간단한 함수를 1개의 문장으로 정의해 사용한다.
statment_function(v1,v2,..., vn) = expression
...
variable = statment_function(a1,a2,..., an)
program statement_function
implicit none
integer :: a, b
integer :: plus_one
real(8) :: e, m
real(8), parameter :: c=299792458d0
plus_one(a) = a + 1
e(m) = m*c**2
a = 10
b = plus_one(a)
print *, a, b
m = 1d-3
print *, e(m)
end program statement_function
$ ./a.out
10 11
89875517873681.766
Interface block
- Example - implicit interface
program implicit
implicit none
real :: i=3d0, j=25d0
real :: ratio
print *, ratio(i,j)
end program implicit
real function ratio(x,y)
real :: x, y
ratio = x/y
end function ratio
$ ./a.out
0.119999997
- Example - explicit interface
program explicit
implicit none
interface
real function ratio(x,y)
real :: x, y
end function ratio
end interface
real :: i=3d0, j=25d0
print *, ratio(i,j)
end program explicit
real function ratio(x,y)
real :: x, y
ratio = x/y
end function ratio
$ ./a.out
0.119999997
- Example - internal procedure
program internal
implicit none
real :: i=3d0, j=25d0
print *, ratio(i,j)
contains
real function ratio(x,y)
real :: x, y
ratio = x/y
end function ratio
end program internal
$ ./a.out
0.119999997