fd1d_predator_prey, a FORTRAN90 code which solves a predator-prey system in a one dimensional region, creating graphics files for processing by GNUPLOT, by Marcus Garvie.
The code requires both some interactive input from the user, and two simple routines that define the initial values.
The nondimensional problem has the form
du/dt = del u + ( 1 - u ) * u - v * h(u/alpha)
dv/dt = delta * del v - gamma * v + beta * v * h(u/alpha)
with initial conditions:
u(x,0) = u0(x)
v(x,0) = v0(x)
and boundary conditions at the left and right endpoints [A,B]:
du/dx = 0
dv/dx = 0
The Type II functional response employed here is
h(eta) = eta / ( 1 + eta )
The parameters ALPHA, BETA, GAMMA and DELTA are strictly positive.
The user must input a value H specifying the desired space step to be used in discretizing the space dimension.
A finite difference scheme is employed to integrate the problem from time 0 to a maximum time T. The user must input the value T, as well as an appropriate time step DELT.
A typical input for this problem is:
ALPHA = 0.3
BETA = 2.0
GAMMA = 0.8
DELTA = 1.0
A = 0.0
B = 200.0
H = 0.5
T = 40.0
DELT = 0.0104
GAUSS = 0 (0 = direct solution, 1 = Jacobi )
with the following initial values of U and V supplied in
auxiliary subroutines:
u0(1:n) = exp ( - ( x(1:n) - 100.0 )**2 ) / 5.0
v0(1:n) = 2.0 / 5.0
The user is prompted for all the necessary parameters, time and space-steps. The formulas for the initial values of the functions U and V must be supplied by two FORTRAN90 subroutines.
The computer code and data files made available on this web page are distributed under the MIT license
fd1d_predator_prey is available in a FORTRAN90 version and a MATLAB version.
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Marcus Garvie