Fortraneries/GravityField/realfield.f90

210 lines
6.2 KiB
Fortran

!-----------------------------------------------------------------------
!-
! some functions for the project "gravity field"
!-
!-----------------------------------------------------------------------
module realfield
use spitpgm ! XXX
implicit none
!-----------------------------------------------------------------------
!-
! definition of structures
!-
type massbody
real :: posx = 0, posy = 0
real :: heading = 0.29
real :: speed = 1.017
real :: mass = 1.0
integer :: serial = 666
end type
!-----------------------------------------------------------------------
contains
!-----------------------------------------------------------------------
subroutine compute_barycentre_bodies(astres, bcx, bcy)
type(massbody), intent(in) :: astres(:)
real, intent(out) :: bcx, bcy
integer :: foo
real :: cx, cy
! May be we have to use DOUBLE RPECSION here ?
cx = 0.0
cy = 0.0
do foo=1, ubound(astres, 1)
cx = cx + astres(foo)%posx
cy = cy + astres(foo)%posy
enddo
bcx = cx / real(ubound(astres, 1))
bcy = cy / real(ubound(astres, 1))
end subroutine
!-----------------------------------------------------------------------
subroutine print_barycentre_bodies(astres)
type(massbody), intent(in) :: astres(:)
real :: cx, cy
call compute_barycentre_bodies(astres, cx, cy)
print *, "barycentre : ", cx, cy
end subroutine
!-----------------------------------------------------------------------
!-
! make a few solid body to play with...
!-
! planets : an array of type(massbody) to be filled
! coef : for setting the mass of the body
! sx, sy : borders of the universe
!-
subroutine create_some_planets(planets, coef, sx, sy)
type(massbody), intent(inout) :: planets(:)
real, intent(in) :: coef
integer, intent(in) :: sx, sy
integer :: foo
character(100) :: fmt
fmt = "(I4, ' | ', 2(F10.2, ' '), ' | ', 2F9.3, ' ', e12.3, I7)"
do foo=1, ubound(planets, 1)
if (foo .EQ. 1) then
!-
! the first planet is the home of Johnny Root
!-
planets(1)%posx = sx / 2
planets(1)%posy = sy / 2
planets(1)%mass = 29e8
planets(1)%serial = 1337
planets(1)%speed = 6.666
else
!-
! others are planets for peones
!-
planets(foo)%posx = rand() * real(sx-1)
planets(foo)%posy = rand() * real(sy-1)
planets(foo)%mass = 7e6 + coef*foo
planets(foo)%heading = 3.14159 * rand()
if (rand() .LT. 0.08) planets(foo)%speed = 3.14159
planets(foo)%serial = foo*2 + 120
endif
write (*, fmt) foo, planets(foo)
enddo
end subroutine
!-----------------------------------------------------------------------
!-
! the basis of the kluge
!-
function compute_gravity(fx, fy, body)
real, intent(in) :: fx, fy
type(massbody), intent(in) :: body
real :: compute_gravity
real :: rx, ry, dist
rx = fx - body%posx
ry = fy - body%posy
dist = sqrt( (rx*rx) + (ry*ry) )
if (dist .LT. 0.08) then
! write (0, *) "dist too small ", dist
compute_gravity = 0e0
else
compute_gravity = body%mass / (dist ** 2)
endif
end function
!-----------------------------------------------------------------------
!-
! Compute the gravity field in a pre-allocated array relative
! to the massbody 'moon'. Nobody know where the magic number
! come from, sorry.
!-
subroutine compute_a_field(field, moon)
real, dimension(:,:), intent(out) :: field
type(massbody), intent(in) :: moon
integer :: ix, iy
real :: fx, fy
real :: grav
! print *, "pic size ", ubound(field, 1), "W", ubound(field, 2), "H"
! print *, "mass body ", moon
do ix=1, ubound(field, 1)
fx = real(ix)
do iy=1, ubound(field, 2)
fy = real(iy)
grav = compute_gravity(fx, fy, moon)
field(ix,iy) = grav
enddo
enddo
end subroutine
!-----------------------------------------------------------------------
!-
! compute a field with only one body; and write a pic file
!-
subroutine build_and_write_a_field(szx, szy, moons, fname)
integer, intent(in) :: szx, szy
type(massbody), intent(in) :: moons(:)
character(len=*), intent(in) :: fname
real :: maxi, mini
integer :: errcode, foo
real, dimension(:,:), allocatable :: field, tmpf
integer, dimension(:,:), allocatable :: greymap
allocate(field(szx, szy), stat=errcode)
allocate(tmpf(szx, szy), stat=errcode)
field = 0.0
do foo=1, ubound(moons, 1)
call compute_a_field(tmpf, moons(foo))
tmpf = tmpf * 0.019
field = field + tmpf
enddo
maxi = maxval(field)
mini = minval(field)
! print *, "field: ", mini, maxi, maxi-mini
allocate(greymap(szx, szy), stat=errcode)
greymap = 65533
! convert from real value to 16 bits int values
where (field < 65530.0)
greymap = int(field)
end where
call spit_as_pgm_16(greymap, trim(fname))
! make valgrind happy
deallocate(field)
deallocate(greymap)
end subroutine
!-----------------------------------------------------------------------
!-
! Yes, I know, this is a disturbing kluge, but I like it :}
! May be, it's time to read the doc of modern Fortran
!-
subroutine init_random()
integer, dimension(3) :: tarray
integer :: t3
real :: dummy
call itime(tarray)
t3 = 8971*tarray(1) + 443*tarray(2) + tarray(3)
write(0, '(A,3I3,A,I6)') "sranding: ", tarray, " --> ", t3
call srand(t3)
! after initializing the random generator engine,
! you MUST use it for initializing the initializer
do t3=1, 4
dummy = rand()
write(0, *) 'dummy ', t3, dummy
enddo
end subroutine
!-----------------------------------------------------------------------
!-----------------------------------------------------------------------
end module