### layout-spring

#### layout-spring turtle-set link-set spring-constant spring-length repulsion-constant

Arranges the turtles in turtle-set, as if the links in link-set are springs and the turtles are repelling each other. Turtles that are connected by links in link-set but not included in turtle-set are treated as anchors and are not moved.

spring-constant is a measure of the "tautness" of the spring. It is the "resistance" to change in their length. spring-constant is the force the spring would exert if it's length were changed by 1 unit.

spring-length is the "zero-force" length or the natural length of the springs. This is the length which all springs try to achieve either by pushing out their nodes or pulling them in.

repulsion-constant is a measure of repulsion between the nodes. It is the force that 2 nodes at a distance of 1 unit will exert on each other.

The repulsion effect tries to get the nodes as far as possible from each other, in order to avoid crowding and the spring effect tries to keep them at "about" a certain distance from the nodes they are connected to. The result is the laying out of the whole network in a way which highlights relationships among the nodes and at the same time is crowded less and is visually pleasing.

The layout algorithm is based on the Fruchterman-Reingold layout algorithm. More information about this algorithm can be obtained here.

    to make-a-triangle
      set-default-shape turtles "circle"
      crt 3
      ask turtle 0
      [
        create-links-with other turtles
      ]
      ask turtle 1
      [
        create-link-with turtle 2
      ]
      repeat 30 [ layout-spring turtles links 0.2 5 1 ] ;; lays the nodes in a triangle
    end

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