!*******************************************************************
! file:        parameters.f90
! language:    f90
! author:      Emma Falck
! updated:     April, 23
! description: A module containing the (input) parameters for 
!              meso.f90.
!********************************************************************
! The author of this software is E. Falck. Copyright (c) 2002.
! Permission to use, copy, modify, and distribute this software for 
! any purpose without fee is hereby granted, provided that this entire
! notice is included in all copies of any software which is or includes
! a copy or modification of this software and in all copies of the 
! supporting documentation for such software.
! THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR 
! IMPLIED WARRANTY. IN PARTICULAR, NEITHER THE AUTHOR NOR SOFTSIMU 
! MAKE ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE 
! MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR 
! PURPOSE.
!*******************************************************************

MODULE parameters

  IMPLICIT NONE

!-------------------------------------------------------------------
! The global parameters are distinguished from local variables
! by the use of capital letters. 
!-------------------------------------------------------------------

!-------------------------------------------------------------------
! To be used in variable declarations.
!-------------------------------------------------------------------

  INTEGER, PARAMETER :: &           
      DP = KIND(1.0D0) 

!-------------------------------------------------------------------
! Auxiliary variables needed in initialization.
!-------------------------------------------------------------------

  INTEGER :: &
      ia                            ! array index

!-------------------------------------------------------------------
! Constants.
!-------------------------------------------------------------------
  
  REAL(DP), PARAMETER :: &
      PI_D = 3.141592653589793238462643383279502884197_dp, &
      PIO2_D = 1.57079632679489661923132169163975144209858_dp, &
      TWOPI_D = 6.283185307179586476925286766559005768394_dp

!--------------------------------------------------------------------
! Parameters.
!--------------------------------------------------------------------

  INTEGER, PARAMETER :: &
      CHECKSTEPS = 10, &            ! n. of steps between checking \beta etc.
      COLSTEPS = 4000, &            ! number of steps after equilibration
      CONFSTEPS = 100, &            ! time interval for saving configurations
      DIM = 2, &                    ! dimension of the system
      EQSTEPS = 500, &              ! number of equilibration steps 
      INCSTEPS = 1, &               ! number of steps between samples
      MAXSTR = 30, &                ! maximum lentgth of character string
      MAXSTRAC = 20, &              ! max. n. of elem. in stress a.c. f.
      MAXVCMAC = 100, &             ! max. n. of elem. in c. of m. vel. a.c. f
      NSE = 20, &                   ! number of solute particles
      MAXNAB = 50 * NSE, &          ! number of elements in Verlet list      
      NST = 910, &                  ! number of solvent particles
      NWSX = 20, &                  ! number of coll. vol.'s in x dir.
      NWSY = 20, &                  ! number of coll. vol.'s in y dir.
      RSEED = 60202, &              ! integer seed for the rng
      TEMPSTEPS = 1000, &           ! number of steps for tempering
      X  = 1, &                     ! coordinate index for vectors
      Y  = 2                        ! coordinate index for vectors

  REAL(DP), PARAMETER :: &
      BETA = 1._dp / 1.2_dp, &      ! 1 / (k_B T)
      DT = 0.005_dp, &              ! time step for MD
      EPS = 1._dp, &                ! LJ parameter, unit of energy
      INITDIST = 1.04245_dp, &      ! initial distance between monomers
      KB = 10._dp, &                ! spring constant
      LB = 1._dp, &                 ! equilibrium distance in spring pot.
      MAXINITANG = 0.9_dp * PI_D, & ! max. ang. for init. displ. n.-n.
      MININITANG = 0.1_dp * PI_D, & ! min. ang. for init. displ. n.-n.
      MST = 1._dp, &                ! solvent mass, mass unit
      MSE = 2._dp * MST, &          ! solute mass
      RCUT = &                      ! cutoff radius for LJ potential
      1.122462048309_dp, &   
      RLIST = 4._dp, &              ! skin size
      SIG = 1._dp, &                ! LJ parameter, unit of length
      TAU = 1._dp, &                ! time step for collision dynamics     
      TAULJ = 1._dp, &              ! LJ time, time unit
      UMEAN = 0._dp                 ! mean velocity of the system

  REAL(DP), DIMENSION(1:DIM), PARAMETER :: &
      LENG = (/ &                   ! linear sizes in all directions
      40._dp, &                     ! linear size in x-direction
      40._dp /)                     ! linear size in y-direction

  CHARACTER(LEN = MAXSTR), PARAMETER :: &
      MPREFIX = 'monom', &          ! prefix for outputting coordinates
      POSTFIX = '.dat'              ! postfix for outputting conf.'s

  CHARACTER(LEN = *), PARAMETER :: &
      CONFFORM = '(2F30.15)', &     ! form factor for outputting a conformation
      NAMEFORM = '(I30)', &         ! form for naming files
      VECFORM = '(3F30.15)'         ! form factor for outputting vectors

!--------------------------------------------------------------------
! Parameters computed from parameters. :)
!--------------------------------------------------------------------

  INTEGER, PARAMETER :: &
      MAXCHECK = &                  ! max. n. of elements in "checking arrays"
      COLSTEPS / CHECKSTEPS, &
      MDSTEPS = int(TAU / DT), &    ! number of MD steps between collisions
      N = NST + NSE, &              ! total number of particles
      NWS = NWSX * NWSY, &          ! number of collision volumes         
      TOTSTEPS = &                  ! total number of steps
      COLSTEPS + EQSTEPS

  REAL(DP), PARAMETER :: &
      LWS = LENG(X) / NWSX, &       ! lin. size of collision volume
      RHO = &                       ! solvent number density
      N / (LENG(X) * LENG(Y))

END MODULE parameters