/usr/share/doc/plotutils/ode/population.ode is in plotutils 2.6-3ubuntu1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | # This is an example from population biology (the predator-prey
# equations of Lotka and Volterra). You may run it by doing:
#
# ode < population.ode | graph -T X -C
#
# or alternatively, to get a real-time plot,
#
# ode < population.ode | graph -T X -C -x 0 10 -y 0 3
#
# The plot shows the population of the prey as a function of time.
# The curve oscillates, because as the prey die out, the predators
# starve.
# The differential equations are:
# x' = (A - By) x
# y' = (Cx - D) y
# A,B,C,D > 0
x' = (A - B*y) * x
y' = (C*x - D) * y
A = 1
B = 1
C = 1
D = 1
x = 3
y = 1
print t, x
step 0, 10
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