Update flood_fill.f90

!

!-------------------------------------------------------------------------------------

! This is a 2D code, assume the system size is

! System_Size(1)xSystem_Size(2)xSystem_Size(3)

! yita is an array of the order parameters in phase-field models, and

! area is the return array containing the area (in 3D the volume). 

! MAXPN is the max number of particles in the domain

! This is a subroutine for identify particles in a 2D domain, assume the system size is

! System_Size(1)xSystem_Size(2)xSystem_Size(3), where System_Size(1)=1 (two-dimensional). 

! 'yita' is an array of the order parameters imported from phase-field models, and

! 'area' is the return array containing the area (in 3D the volume). 

! MAXPN is the maximum possible number of particles in the domain. 

Subroutine flood_fill_PSD(yita, area)