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# This example simulates two similar pendulums, coupled with a horizontal
# spring. The motion is taken to be undamped.
#
# The plot shows the displacement of one of the pendulums, as a function of
# time. It illustrates how energy (e.g. maximum displacement) oscillates
# back and forth between the two.
# You may run this example by doing:
#
# ode < coupled.ode | graph -T X -C
#
# or alternatively, to get a real-time plot,
#
# ode < coupled.ode | graph -T X -C -x 0 50 -y -0.6 0.6
# The equations are:
# m*x1'' = - m*g*x1/l + k(x2 - x1)
# m*x2'' = - m*g*x2/l - k(x2 - x1)
xone' = vxone
xtwo' = vxtwo
vxone' = -g*xone/lone + k/mone * ( xtwo - xone)
vxtwo' = -g*xtwo/ltwo - k/ltwo * ( xtwo - xone)
k = 1
g = 9.8 # acceleration due to gravity
lone = 5
ltwo = 5
mone = 1
mtwo = 1
xone = 0.0
xtwo = 0.3
vxone = 0
vxtwo = 0
print t, xone
step 0,50
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