new villi food model

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Default-person Michael Novak (Author)


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This model supports a drawing style interface for "sketching" up representations of new systems to explore related to gas behavior and gas particles. This model is part of the "Connected Chemistry" curriculum which explores the behavior of gases.

Most of the models in the Connected Chemistry curriculum use the same basic rules for simulating the behavior of gases. Each model highlights different features of how gas behavior is related to gas particle behavior.

In all of the models, gas particles are assumed to move and to collide, both with each other and with objects such as walls.

In this model, particles can be added, color coded, and sped up or slowed down, by drawing with the mouse cursor in the WORLD & VIEW. Also, additional types of removable and replaceable walls can be added to the WORLD.

This model enables students to draw a model of a real world system and then test that model. A wide range of real world systems can be modeled with this simple interface (e.g. diffusion of perfume from an uncapped container, hot gas mixed with a cold gas, mixtures of gases).


The particles are modeled as hard balls with no internal energy except that which is due to their motion. Collisions between particles are elastic. Collisions with the wall are not.

The exact way two particles collide is as follows:

  1. A particle moves in a straight line without changing its speed, unless it collides with another particle or bounces off the wall.
  2. Two particles "collide" if they find themselves on the same patch. In this model, two turtles are aimed so that they will collide at the origin.
  3. An angle of collision for the particles is chosen, as if they were two solid balls that hit, and this angle describes the direction of the line connecting their centers.
  4. The particles exchange momentum and energy only along this line, conforming to the conservation of momentum and energy for elastic collisions.
  5. Each particle is assigned its new speed, heading and energy.

As the walls of the box are heated, the sides of the walls will change color from a deep red (cool) to a bright red, to pink to a pale pink white (hot). The walls contain a constant heat value throughout the simulation.

The exact way particles gain energy from the walls of the box is as follows:

  1. Particles check their state of energy (kinetic).
  2. They hit or bounce off the wall.
  3. They find wall energy and set their new energy to be the average of their old kinetic energy and the wall energy.
  4. They change their speed and direction after the wall hit.


Buttons: SETUP - sets up the initial conditions set on the sliders. GO/STOP - runs and stops the model. MOUSE INTERACTION - when this is set to "none - let the particles interact" the particles will move and interact with each other and the surroundings. When set to any other value you can then click in the WORLD & VIEW to paint, erase, color, or add various objects and properties.

Sliders: INITIAL-#-PARTICLES - sets the number of gas particles in the box when the simulation starts. INITIAL-GAS-TEMPERATURE sets the initial temperature of the gas.

Switches: SHOW-WALL-HITS? turn visualization of when particles hits the walls (as flashes) on or off

Choosers: VISUALIZE-SPEED? allows you to visualize particle speeds. For example, selecting "arrows", creates a representation of each particle velocity using a scalar arrow. Selecting "shades" creates representation of each particle speed using a brighter (faster) or darker (slower) shade of the particle's color.

MOUSE-INTERACTION sets the type interaction the user can do with the mouse in the WORLD & VIEW. Possible settings include: "none - let the particles interact" - particles move about "draw basic wall" - adds a gray wall under the mouse cursor "draw red removable wall" - adds a red wall under the mouse cursor which can be alternatively removed and replaced (like a valve) using the REMOVE/REPLACE RED WALL. "draw green removable wall" - adds a green wall under the mouse cursor which can be alternatively removed and replaced (like a valve) using the REMOVE/REPLACE GREEN WALL. "big eraser" - erases all objects (except the yellow box boundary walls) under the mouse cursor. "slow down particles" - increase the current speed of the particles by 10%. "speed up particles" - reduces the current speed of the particles by 10%. "paint particles green" - recolors the particles under the mouse cursor green (other settings include orange and purple) "add green particles" - adds a couple of new particles under the mouse cursor (other settings include orange and purple)


  • 1: TEMPERATURE OF GASES VS. TIME: plots the temperature of the different gases in the model, as indicated by their color (orange particles, green particles, and purple particles)


The mouse interaction can be used while the model is running as well as when it is stopped.


Create a model of how odors move throughout a room. Why do some people smell the odor before others? Does the layout of furniture, large objects, and walls in the room effect the movement of the odor? How about the temperature of the air in the room?

Create a model of diffusion of a perfume from a closed container. How would you represent the different gases (the perfume and the surrounding air)? What shape will the container be? How will you model a removable cap or lid?

Create a model of room filled with cold air and a different room filled with warm air. How will represent these different rooms of air? What could you add to show what happens when they mix?

Create a model of heat transfer that shows what happens to the energy of one very fast moving gas particle when it hits a bunch of very slow moving gas particles. What does this show happening to the energy of the initial gas particles?


See GasLab Models See other Connected Chemistry models.


This model is part of the Connected Chemistry curriculum. See

We would like to thank Sharona Levy and Michael Novak for their substantial contributions to this model.


If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the model itself:

Please cite the NetLogo software as:

To cite the Connected Chemistry curriculum as a whole, please use:


Copyright 2006 Uri Wilensky.


This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at

Comments and Questions

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Click to Run Model

globals [
  tick-advance-amount               ; how much we advance the tick counter this time through
  max-tick-advance-amount           ; the largest tick-advance-amount is allowed to be
  init-avg-speed init-avg-energy    ; initial averages
  avg-speed avg-energy              ; current average

breed [ particles particle ]
breed [ flows flow ]
breed [ walls wall ]
breed [ edges edge ]

particles-own [
  speed mass energy          ; particles info

patches-own [


walls-own [

to setup
  ask patches [set pcolor white]
  set particle-size 2
  set max-tick-advance-amount 0.02
  set show-wall-hits? false
  set particles-to-add 2
  set old-villi-slider-value villi-height
  set villi-slider-moved? true
  set bottom-wall-ycor min-pycor + 3
  set-default-shape walls "cell"
  set max-particles 200
  set #-green-particles 0
  set #-purple-particles 0
  set #-orange-particles 0
  set tracker-init-particles initial-#-small-food-particles
  set permeability 50
  set particle-to-watch nobody

  set min-particle-energy 0
  set max-particle-energy 500  ;(.5 ) * ( max-dist-in-tick-advance-amount  / max-tick-advance-amount ) ^ 2

  set  total-initial-particles count particles
  set  total-absorbed-particles 0

  set init-avg-speed avg-speed
  set init-avg-energy avg-energy


to go

  if ticks < end-simulation-at [

    ask particles with [not absorbed?] [ bounce ]
    ask flows [move-flows]
    ask particles with [not absorbed?] [ move ]
    ask particles with [absorbed?  and pycor != min-pycor] [seep-toward-blood]
    ask particles with [swept?] [sweep-with-blood]
  ;  ask particles with [not absorbed?] [ check-for-collision ]
    ask particles with [not absorbed? and any? walls-here ] [ rewind-to-bounce ]
    ask particles with [not absorbed? and any? walls-here ] [ remove-from-walls ]


  tick-advance tick-advance-amount


to check-watched-particle
  if particle-to-watch != nobody [
  ask particle-to-watch [
      if pycor = max-pycor [rp]


to check-particle-flow-out-of-system
  ask particles [
    if pxcor = max-pxcor and visualize-food-in-blood-flow-as = "going someplace else" [set total-absorbed-particles total-absorbed-particles + 1 set hidden? true]

to update-variables
  let green-particles particles with [ color-type = 55 ]
  let purple-particles  particles with [ color-type = 115 ]
  let orange-particles particles with [ color-type = 25 ]
  set #-green-particles count green-particles
  set #-orange-particles count orange-particles
  set #-purple-particles count purple-particles
  set #particles (#-green-particles + #-purple-particles + #-orange-particles)

  if any? particles [
    set avg-speed  mean [ speed ] of particles
    set avg-energy mean [ energy ] of particles

  ifelse #-green-particles > 0 [
    set avg-energy-green mean [ energy ] of green-particles
  [ set avg-energy-green "N/A"]

  ifelse  #-orange-particles > 0 [
    set avg-energy-orange mean [ energy ] of orange-particles
  [ set avg-energy-orange "N/A"]

  ifelse  #-purple-particles > 0 [
    set avg-energy-purple mean [ energy ] of purple-particles
  [ set avg-energy-purple "N/A"]

to watch-a-particle
  set particle-to-watch one-of particles with [pycor < (max-pycor - 2)]
  if count particles > 0 [
    watch one-of particles


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;BUILD VILLI   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to shove-particles
  ask particles-here with [pycor <= (bottom-wall-ycor + villi-height)] [set ycor (bottom-wall-ycor + villi-height)]

to add-wall
          sprout 1 [
          set breed walls set color gray
          ;set is-blood? false

to add-hidden-wall
          sprout 1 [
          set breed walls set color gray
          set is-blood? false
          set hidden? true

to initialize-blood
          set breed walls set color red
          set size 1.0
          set is-blood? true
          set heading 90
          set shape "square"
          set color [255 0 0 150]

to add-blood-up
  set blood-heading 0
  set is-blood? true
  sprout 1 [initialize-blood ]

to add-blood-down
  set blood-heading 180
  set is-blood? true
  sprout 1 [initialize-blood]

to add-blood-right
  set blood-heading 90
  set is-blood? true
  sprout 1 [initialize-blood]

to redraw-villi?
  if old-villi-slider-value != villi-height [set villi-slider-moved? true set old-villi-slider-value villi-height]
  if villi-slider-moved? [
     set villi-slider-moved? false

to redraw-villi
  ask walls with [pycor >= (min-pycor + 3)] [die]
  ask patches with [pycor >= (min-pycor + 3)] [set is-blood? false]
   ;; draw horizontal line until reaching a point where a villi is... then call villi build...skip and continue

   let distance-between-villi 5

    ask patches with [pxcor >= min-pxcor and pxcor <= max-pxcor and pycor = max-pycor ]  [add-hidden-wall]

     let this-pxcor min-pxcor
     let this-pycor bottom-wall-ycor
     let villi-width 5
     let this-width-counter 0
     let this-lift false
   repeat (max-pxcor - min-pxcor + 1)  [

    ifelse ((this-pxcor mod 11 >= 0) and (this-pxcor mod 11 <= 4)) and (this-pxcor >= (min-pxcor + 3) and this-pxcor <= (max-pxcor - 5))
         [set this-pycor (bottom-wall-ycor + villi-height) set this-lift true]
         [set this-pycor bottom-wall-ycor]
    ask patches with [pxcor = this-pxcor and pycor = this-pycor] [add-wall]

    ;; draw-vertical wall
    if this-lift [
        ask patches with [pxcor = this-pxcor and pycor >= bottom-wall-ycor and pycor <= this-pycor] [
          if (this-pxcor mod 11 = 0 and pycor < (this-pycor)) [add-wall]
          if (this-pxcor mod 11 = 1 and pycor < (this-pycor - 1)) [add-blood-up]
          if (this-pxcor mod 11 = 2 and pycor < (this-pycor - 2))[add-wall]
          if ((this-pxcor mod 11 = 2 or this-pxcor mod 11 = 1) and (pycor = (this-pycor - 1) ))[add-blood-right]
         if ((this-pxcor mod 11 = 2 ) and ( pycor = (this-pycor - 2)))[add-blood-right]
          if (this-pxcor mod 11 = 3 and pycor <= (this-pycor - 1)) [add-blood-down]
          if (this-pxcor mod 11 = 4 and pycor < (this-pycor)) [add-wall]
      set this-lift false
    set this-pxcor this-pxcor + 1

to draw-blood-stream
  let blood-patches patches with [pxcor >= min-pxcor and pxcor <= max-pxcor and pycor < bottom-wall-ycor and pycor >= min-pycor ]
  ask blood-patches [add-blood-right]
  ask n-of 30 blood-patches [

to make-a-floater
  let this-color (5 + random-float 20)
  let this-list [0 0 0]
  set this-list lput  this-color this-list
  sprout 1 [
    set breed flows
  set color this-list
  set shape "square"

to draw-edges
  ask patches with [pycor = (max-pycor) and pxcor < max-pxcor ][
    sprout 1 [
      set breed edges
      set shape "square 3"
      set size 1.05
      set color gray + 2
   ask patches with [pycor < (max-pycor) and pxcor = max-pxcor ][
    sprout 1 [
      set breed edges
      set shape "square 4"
      set size 1.05
      set color gray + 2
     ask patches with [pycor =(max-pycor) and pxcor = max-pxcor ][
     sprout 1 [
      set breed edges
      set shape "square"
      set size 1.05
      set color gray + 2

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;WALL INTERACTION;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;GAS MOLECULES MOVEMENT;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to bounce  ; particles procedure
  ; get the coordinates of the patch we'll be on if we go forward 1
  let bounce-patch nobody
  let bounce-patches nobody
  let hit-angle 0
  let this-patch patch-here
  let new-px 0
  let new-py 0
  let visible-wall nobody

  set bounce-patch  min-one-of walls in-cone ((sqrt (2)) / 2) 180 with [ patch-here != this-patch ] [ distance myself ]

  if bounce-patch != nobody [
    set new-px [ pxcor ] of bounce-patch
    set new-py [ pycor ] of bounce-patch
    set visible-wall walls-on bounce-patch

    if any? visible-wall  [
      ifelse (random 100 > permeability or (pycor >= (max-pycor - 1) ) or large? ) [
      if bounce-patch != patch-here [ set hit-angle towards bounce-patch ] ;; new bounce patch code
      ifelse (hit-angle <= 135 and hit-angle >= 45) or (hit-angle <= 315 and hit-angle >= 225) [
        set heading (- heading)
        set heading (180 - heading)

      set absorbed? false]
      [set absorbed? true]


to rewind-to-bounce  ; particles procedure
  ; attempts to deal with particle penetration by rewinding the particle path back to a point
  ; where it is about to hit a wall
  ; the particle path is reversed 49% of the previous tick-advance-amount it made,
  ; then particle collision with the wall is detected again.
  ; and the particle bounces off the wall using the remaining 51% of the tick-advance-amount.
  ; this use of slightly more of the tick-advance-amount for forward motion off the wall, helps
  ; insure the particle doesn't get stuck inside the wall on the bounce.

  let bounce-patch nobody
  let bounce-patches nobody
  let hit-angle 0
  let this-patch nobody
  let new-px 0
  let new-py 0
  let visible-wall nobody

  bk (speed) * tick-advance-amount * .49
  set this-patch  patch-here

  set bounce-patch  min-one-of walls in-cone ((sqrt (2)) / 2) 180 with [ self != this-patch ] [ distance myself ]

  if bounce-patch != nobody [

    set new-px [pxcor] of bounce-patch
    set new-py [pycor] of bounce-patch
    set visible-wall walls-on bounce-patch

    if any? visible-wall with [not hidden?] [
      set hit-angle towards bounce-patch

      ifelse (hit-angle <= 135 and hit-angle >= 45) or (hit-angle <= 315 and hit-angle >= 225) [
        set heading (- heading)
        set heading (180 - heading)

  fd (speed) * tick-advance-amount * 0.75

to move  ; particles procedure
  if patch-ahead (speed * tick-advance-amount) != patch-here [ set last-collision nobody ]
  ifelse (not large?) [rt random 30 lt random 30][rt random 10 lt random 10]
  fd (speed * tick-advance-amount * 0.75)
  if ycor >  (bottom-wall-ycor + villi-height) [set xcor xcor - .05]

to move-flows
  set heading 90
  fd (7 * tick-advance-amount * 0.75)

to seep-toward-blood
  let flex-threshold .2 + random-float .05
  let all-blood patches with [is-blood?]
  let target-blood-patch min-one-of all-blood [distance myself  ]
 ; show distance target-blood
  let final-heading towards target-blood-patch
  let heading-difference ((final-heading - heading) / 20)
  set heading heading + heading-difference
  let blood-near-me all-blood with [distance myself < flex-threshold]
  ifelse not any? blood-near-me [fd (2 * tick-advance-amount) ][set swept? true]

to sweep-with-blood
  let old-heading heading
  let heading-difference ((old-heading - heading) / 20)
  if (is-blood? and swept?)  [set heading blood-heading fd (3 * tick-advance-amount) set heading heading + heading-difference]

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;GAS MOLECULES COLLISIONS;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;from GasLab

to calculate-tick-advance-amount
  ; tick-advance-amount is calculated in such way that even the fastest
  ; particles will jump at most 1 patch delta in a ticks tick. As
  ; particles jump (speed * tick-advance-amount) at every ticks tick, making
  ; tick delta the inverse of the speed of the fastest particles
  ; (1/max speed) assures that. Having each particles advance at most
  ; one patch-delta is necessary for it not to "jump over" a wall
  ; or another particles.
  ifelse any? particles with [ speed > 0 ] [
    set tick-advance-amount min list (1 / (ceiling max [speed] of particles )) max-tick-advance-amount
    set tick-advance-amount max-tick-advance-amount

to check-for-collision  ; particles procedure
  ; Here we impose a rule that collisions only take place when there
  ; are exactly two particles per patch.  We do this because when the
  ; student introduces new particles from the side, we want them to
  ; form a uniform wavefront.
  ; Why do we want a uniform wavefront?  Because it is actually more
  ; realistic.  (And also because the curriculum uses the uniform
  ; wavefront to help teach the relationship between particles collisions,
  ; wall hits, and pressure.)
  ; Why is it realistic to assume a uniform wavefront?  Because in reality,
  ; whether a collision takes place would depend on the actual headings
  ; of the particles, not merely on their proximity.  Since the particles
  ; in the wavefront have identical speeds and near-identical headings,
  ; in reality they would not collide.  So even though the two-particles
  ; rule is not itself realistic, it produces a realistic result.  Also,
  ; unless the number of particles is extremely large, it is very rare
  ; for three or  particles to land on the same patch (for example,
  ; with 400 particles it happens less than 1% of the time).  So imposing
  ; this additional rule should have only a negligible effect on the
  ; aggregate behavior of the system.
  ; Why does this rule produce a uniform wavefront?  The particles all
  ; start out on the same patch, which means that without the only-two
  ; rule, they would all start colliding with each other immediately,
  ; resulting in much random variation of speeds and headings.  With
  ; the only-two rule, they are prevented from colliding with each other
  ; until they have spread out a lot.  (And in fact, if you observe
  ; the wavefront closely, you will see that it is not completely smooth,
  ; because  collisions eventually do start occurring when it thins out while fanning.)

  if count other particles-here  in-radius 1 = 1 [
    ; the following conditions are imposed on collision candidates:
    ;   1. they must have a lower who number than my own, because collision
    ;      code is asymmetrical: it must always happen from the point of view
    ;      of just one particles.
    ;   2. they must not be the same particles that we last collided with on
    ;      this patch, so that we have a chance to leave the patch after we've
    ;      collided with someone.
    let candidate one-of other particles-here with [ who < [ who ] of myself and myself != last-collision ]
    ;; we also only collide if one of us has non-zero speed. It's useless
    ;; (and incorrect, actually) for two particles with zero speed to collide.
    if (candidate != nobody) and (speed > 0 or [ speed ] of candidate > 0) [
      collide-with candidate
      set last-collision candidate
      ask candidate [ set last-collision myself ]

; implements a collision with another particles.
; The two particles colliding are self and other-particles, and while the
; collision is performed from the point of view of self, both particles are
; modified to reflect its effects. This is somewhat complicated, so I'll
; give a general outline here:
;   1. Do initial setup, and determine the heading between particles centers
;      (call it theta).
;   2. Convert the representation of the velocity of each particles from
;      speed/heading to a theta-based vector whose first component is the
;      particle's speed along theta, and whose second component is the speed
;      perpendicular to theta.
;   3. Modify the velocity vectors to reflect the effects of the collision.
;      This involves:
;        a. computing the velocity of the center of mass of the whole system
;           along direction theta
;        b. updating the along-theta components of the two velocity vectors.
;   4. Convert from the theta-based vector representation of velocity back to
;      the usual speed/heading representation for each particles.
;   5. Perform final cleanup and update derived quantities.

to collide-with [ other-particles ] ;; particles procedure
  ; PHASE 1: initial setup

  ; for convenience, grab  quantities from other-particles
  let mass2 [ mass ] of other-particles
  let speed2 [ speed ] of other-particles
  let heading2 [ heading ] of other-particles

  ; since particles are modeled as zero-size points, theta isn't meaningfully
  ; defined. we can assign it randomly without affecting the model's outcome.
  let theta (random-float 360)

  ; PHASE 2: convert velocities to theta-based vector representation

  ; now convert my velocity from speed/heading representation to components
  ; along theta and perpendicular to theta
  let v1t (speed * cos (theta - heading))
  let v1l (speed * sin (theta - heading))

  ;; do the same for other-particles
  let v2t (speed2 * cos (theta - heading2))
  let v2l (speed2 * sin (theta - heading2))

  ; PHASE 3: manipulate vectors to implement collision

  ; compute the velocity of the system's center of mass along theta
  let vcm (((mass * v1t) + (mass2 * v2t)) / (mass + mass2) )

  ; now compute the new velocity for each particles along direction theta.
  ; velocity perpendicular to theta is unaffected by a collision along theta,
  ; so the next two lines actually implement the collision itself, in the
  ; sense that the effects of the collision are exactly the following changes
  ; in particles velocity.
  set v1t (2 * vcm - v1t)
  set v2t (2 * vcm - v2t)

  ; PHASE 4: convert back to normal speed/heading

  ; now convert my velocity vector into my new speed and heading
  set speed sqrt ((v1t ^ 2) + (v1l ^ 2))
  set energy (0.5 * mass * speed ^ 2)
  ; if the magnitude of the velocity vector is 0, atan is undefined. but
  ; speed will be 0, so heading is irrelevant anyway. therefore, in that
  ; case we'll just leave it unmodified.
  if v1l != 0 or v1t != 0 [ set heading (theta - (atan v1l v1t)) ]

  ;; and do the same for other-particle
  ask other-particles [
    set speed sqrt ((v2t ^ 2) + (v2l ^ 2))
    set energy (0.5 * mass * (speed ^ 2))
    if v2l != 0 or v2t != 0 [ set heading (theta - (atan v2l v2t)) ]

;;  initialization procedures

to initialize-this-wall
;  set valve-1? false
 ; set valve-2? false
;  set pressure? false
  ifelse random 2 = 0 [set shape "cell"][set shape "cell2"]
  set color [255 255 255 120]
  let turn random 4
  rt (turn * 90)

to make-small-particles
  create-particles initial-#-small-food-particles [
    setup-particles false
    set shape "small-molecule"

to make-large-particles
  create-particles initial-#-large-food-particles [
    setup-particles true
    set shape "large-molecule"

to setup-particles  [is-large]; particles procedure
 ; set shape "circle"
  set size particle-size
  set energy 150
  set color-type (violet - 3)
  set color color-type
  set mass (10)  ; atomic masses of oxygen atoms

  set speed speed-from-energy
  set last-collision nobody
  set absorbed? false
  set large? is-large
  set swept? false

; Place particles at random, but they must not be placed on top of wall atoms.
; This procedure takes into account the fact that wall molecules could have two possible arrangements,
; i.e. high-surface area ot low-surface area.

to random-position ;; particles procedure
  let open-patches nobody
  let open-patch nobody
  set open-patches patches with [not any? turtles-here and pxcor != max-pxcor and pxcor != min-pxcor and pycor != min-pycor and pycor != max-pycor]
  set open-patch one-of open-patches

  ; Reuven added the following "if" so that we can get through setup without a runtime error.
  if open-patch = nobody [
    user-message "No open patches found.  Exiting."

  setxy ([ pxcor ] of open-patch) ([ pycor ] of open-patch)
  set heading random 360
  fd random-float .4

;; wall penetration error handling procedure
; if particles actually end up within the wall

to remove-from-walls
  let this-wall walls-here with [ not hidden? ]

  if count this-wall != 0 [
    let available-patches patches with [ not any? walls-here ]
    let closest-patch nobody
    if (any? available-patches) [
      set closest-patch min-one-of available-patches [ distance myself ]
      set heading towards closest-patch
      setxy ([ pxcor ] of closest-patch)  ([ pycor ] of closest-patch)


to do-plotting


to-report speed-from-energy
  report sqrt (2 * energy / mass)

to-report energy-from-speed
  report (mass * speed * speed / 2)

to-report limited-particle-energy
  let limited-energy energy
  if limited-energy > max-particle-energy [ set limited-energy max-particle-energy ]
  if limited-energy < min-particle-energy [ set limited-energy min-particle-energy ]
  report limited-energy

; Copyright 2006 Uri Wilensky.
; See Info tab for full copyright and license.

There is only one version of this model, created 5 months ago by Michael Novak.

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