from ODESolver import *
import numpy as np
import matplotlib.pyplot as plt

class PredatorPrey:
    def __init__(self,r,m,a,b):
        self.r = r
        self.m = m
        self.a = a
        self.b = b

    def __call__(self, u, t):
        x, y = u[0],u[1]
        r = self.r; m = self.m
        a = self.a; b = self.b

        return r*x-a*x*y, -m*y+b*x*y

problem = PredatorPrey(1,1,0.3,0.2)
solver = RungeKutta4(problem)
solver.set_initial_condition((1,1))
time = np.linspace(0,20,201)

u,t = solver.solve(time)

plt.plot(t,u[:,0],label='Prey pop.')
plt.plot(t,u[:,1],label='Predator pop.')
plt.legend()
plt.show()

"""
Terminal> python predator_prey.py

"""