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! intakes coordinates and outputs index
integer function indexfxn(px, py) result(idx)
double precision, intent(in) :: px, py
double precision :: boxSize,yCoord
integer :: ix, iy
!> Check if particle is in box
if(abs(px).GT.L/2 .OR. abs(py).GT.L/2) then
!> Particle is outside, don't track it
idx=b*b ! This is the "recycle bin" for untracked particles.
else
! the sector size
! M = floor(L / rc)
yCoord = - py
! coordinate + half length of boundary [-L/2,L/2] -> [0,L]
! divided by effective particle size to give coordinate
boxSize=L/real(b,8)
ix = floor((px + L/2.0d0)/boxSize)
iy = floor((yCoord + L/2.0d0)/boxSize)
! for particles on the boundary
ix = min(max(ix, 0), b-1)
iy = min(max(iy, 0), b-1)
if (ix < 0 .or. ix >= b .or. iy < 0 .or. iy >= b) then
print *, "ERROR: particle outside sector grid"
print *, "px, py =", px, py
stop
end if
! call rey's function
idx = TWOtoONE(ix,iy)
end if
end function indexfxn
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