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# This example does a planetary orbit simulation, with two suns situated at
# (0,0) and (-5,0) and one planet starting out at (1,0). You may run it by
# typing
# ode -f orbit.ode | graph -T X -C -y -1 3 -x -6 2
# step 0,10
# step 10,20
# step 20,30
# step 30,40
# step 40,50
# step 50,60
# .
# The planet's orbit will be traced out incrementally. If you are using a
# color X Window System display, each segment of the orbit will be a
# different color. This is a feature provided by `graph', which normally
# changes the linemode after each dataset it reads. If you do not like this
# feature, you may turn it off by using `graph -B' instead of `graph'.
# x and y are positions
# vx and vy are velocities
vx' = -x/((x^2+y^2)^(3/2)) -(x+5)/(((x+5)^2+y^2)^(3/2))
vy' = -y/((x^2+y^2)^(3/2)) -y/(((x+5)^2+y^2)^(3/2))
y' = vy
x' = vx
x = 1
y = 0
print x,y every 5
# these values seem to give a nice orbit:
# vx = 0
# vy = 1.142
# a more exciting result can be obtained from:
vx = 0
vy = 1.165
#step 0,20
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