# host_parasite.py
# =============================================================================
#
# This file is part of SimElements.
# ----------------------------------
#
#  SimElements is a software package designed to be used for continuous and 
#  discrete event simulation. It requires Python 3.0 or later versions.
# 
#  Copyright (C) 2010  Nils A. Kjellbert 
#  E-mail: <info(at)ambinova(dot)se>
# 
#  SimElements is free software: you can redistribute it and/or modify 
#  it under the terms of the GNU General Public License as published by 
#  the Free Software Foundation, either version 3 of the License, or 
#  (at your option) any later version. 
# 
#  SimElements is distributed in the hope that it will be useful, 
#  but WITHOUT ANY WARRANTY; without even the implied warranty of 
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
#  GNU General Public License for more details. 
# 
#  You should have received a copy of the GNU General Public License 
#  along with this program.  If not, see <http://www.gnu.org/licenses/>. 
#
#------------------------------------------------------------------------------
"""
In order for this demo program to work you will probably have to type in one of
the following two paragraphs - or both - depending on your platform and os:

#! /usr/local/bin/python   # ...or what's needed on your computer

from sys import path       # Slashes or backslashes...:
path.append('/Path of directory where you place simelements/simelements')
"""
# And:
newline = '\n'
#  '\n' on Unix and MacOS X, '\r\n' on Windows  and '\r' on Mac Classic
# -----------------------------------------------------------------------------
"""
This program demonstrates how to use dynamic/continuous simulation with
with SimElements to solve a well-known problem known as the host-parasite 
or predator-prey problem.

The dictionary formulation made possible by SimElements' Dynamics class
is used for demonstration.

The output is sent to two tab-delimited text files for further processing 
using standard spreadsheet software or other software suited for graphical 
presentation:
host-parasitep.txt containing numbers with decimal points, and
host-parasitec.txt containing numbers with decimal commas.
"""
# -----------------------------------------------------------------------------

from dynamics          import Dynamics
from misclib.inandout  import writetab

# -----------------------------------------------------------------------------

# Initial population sizes
number_of              =   {}
number_of['hosts']     = 1000.0
number_of['parasites'] =  500.0

# Rate constants
k1 =   0.05     # hosts per host and hour
k2 = - 0.0002   # hosts per parasite, host and hour
k3 = - 0.10     # parasites per parasite and hour
k4 =   0.0002   # parasites per host, parasite and hour


# -- Model is placed in a separate function --------------------

def model(tim, number_of):

    growth_rate = {}
    
    growth_rate['hosts']      =  \
    k1*number_of['hosts']     + k2*number_of['parasites']*number_of['hosts']
    
    growth_rate['parasites']  =  \
    k3*number_of['parasites'] + k4*number_of['hosts']*number_of['parasites']

    return growth_rate

# --------------------------------------------------------------

# Tab-delimited file with decimal point:
points = open('host-parasitep.txt', 'w')

# Tab-delimited file with decimal comma:
commas = open('host-parasitec.txt', 'w')

inputline = "Time\tNo. of hosts\tNo. of parasites" + newline
points.write(inputline)
commas.write(inputline)

tstart =    0.0
tstep  =    0.125
tfin   =  550.0

solution = Dynamics(model, number_of)

tim    = tstart
while tim < tfin:
    tnext = tim + tstep
    tim, number_of  =  solution.rke4(tim, tnext)   # 4th order Runge-Kutta
    if number_of['hosts'] >= 1.0 and number_of['parasites'] >= 1.0:
        inputline  =  tim, number_of['hosts'], number_of['parasites']
        writetab(points, commas, inputline, newline=newline)
    else:
        break

points.close()
commas.close()

print("Results in files host-parasitep.txt and host-parasitec.txt")

# -----------------------------------------------------------------------------