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Multi coupling point masses

Example of generating complex coupling between many nodes. In this example, many nodes are constructed in parallel using name generators (#n3, #n22). Using the same generator syntax, edges can be quickly created between many nodes, in this case bidirectional coupling (spring) between the left and right nodes (#n33).

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g = 9.81

node "n{1:5}{r,l}" {
  m = 1.5

  # Generator syntax also applies to variable names
  "{x,y}" = "rand(-5, 5)"

  x'' = 0

  # External force implementing damping (due to friction)
  Dy = 0.5
  Fy = "-Dy * dy"

  # Acceleration due to gravity plus external force
  y'' = "-g + Fy / m"
}

# We can open up existing nodes and modify them. Here
# we will add a simple fixed spring to the first node on
# both left and right sides
node "n1{r,l}" {
  Ky = 10

  # Set external force to damping plus a spring force
  # pulling back the point mass to 0
  Fy = "-Dy * dy + Ky * -y"
}

# This generates full coupling between the left and right
# nodes
<bidirectional>
edge from "n{1:5}r" to "n{1:5}l" {
  Kx = "5"
  Ky = "20"

  dx' += "Kx * (input.x - output.x) / output.m"
  dy' += "Ky * (input.y - output.y) / output.m"
}

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