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gaslab-test.html
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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>GasLab Test</title>
<link rel="stylesheet" href="dist/highlight-nl.css">
<script src="dist/highlight-nl.min.js"></script>
<script>
window.addEventListener('load', function() {
var elem = document.getElementById('code');
elem.innerHTML = require('highlight-nl')(elem.innerText);
});
</script>
</head>
<body>
<pre style="height: 600px; width: 600px; overflow: scroll; resize: both;" id="code">
globals
[
tick-delta ;; how much we advance the tick counter this time through
max-tick-delta ;; the largest tick-delta is allowed to be
init-avg-speed init-avg-energy ;; initial averages
avg-speed avg-energy ;; current averages
fast medium slow ;; current counts
percent-fast percent-medium ;; percentage of the counts
percent-slow ;; percentage of the counts
]
breed [ particles particle ]
particles-own
[
speed mass energy ;; particle info
last-collision
]
to setup
clear-all
set-default-shape particles "circle"
set max-tick-delta 0.1073
make-particles
update-variables
set init-avg-speed avg-speed
set init-avg-energy avg-energy
reset-ticks
end
to go
ask particles [ move ]
ask particles
[ if collide? [check-for-collision] ]
ifelse (trace?)
[ ask particle 0 [ pen-down ] ]
[ ask particle 0 [ pen-up ] ]
tick-advance tick-delta
if floor ticks > floor (ticks - tick-delta)
[
update-variables
update-plots
]
calculate-tick-delta
display
end
to update-variables
set medium count particles with [color = green]
set slow count particles with [color = blue]
set fast count particles with [color = red]
set percent-medium (medium / count particles) * 100
set percent-slow (slow / count particles) * 100
set percent-fast (fast / count particles) * 100
set avg-speed mean [speed] of particles
set avg-energy mean [energy] of particles
end
to calculate-tick-delta
;; tick-delta is calculated in such way that even the fastest
;; particle will jump at most 1 patch length in a tick. As
;; particles jump (speed * tick-delta) at every tick, making
;; tick length the inverse of the speed of the fastest particle
;; (1/max speed) assures that. Having each particle advance at most
;; one patch-length is necessary for them not to jump over each other
;; without colliding.
ifelse any? particles with [speed > 0]
[ set tick-delta min list (1 / (ceiling max [speed] of particles)) max-tick-delta ]
[ set tick-delta max-tick-delta ]
end
to move ;; particle procedure
if patch-ahead (speed * tick-delta) != patch-here
[ set last-collision nobody ]
jump (speed * tick-delta)
end
to check-for-collision ;; particle procedure
;; Here we impose a rule that collisions only take place when there
;; are exactly two particles per patch.
if count other particles-here = 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 particle.
;; 2. they must not be the same particle 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 ]
]
]
end
;; implements a collision with another particle.
;;
;; THIS IS THE HEART OF THE PARTICLE SIMULATION, AND YOU ARE STRONGLY ADVISED
;; NOT TO CHANGE IT UNLESS YOU REALLY UNDERSTAND WHAT YOU'RE DOING!
;;
;; The two particles colliding are self and other-particle, 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 particle centers
;; (call it theta).
;; 2. Convert the representation of the velocity of each particle 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 particle.
;; 5. Perform final cleanup and update derived quantities.
to collide-with [ other-particle ] ;; particle procedure
;;; PHASE 1: initial setup
;; for convenience, grab some quantities from other-particle
let mass2 [mass] of other-particle
let speed2 [speed] of other-particle
let heading2 [heading] of other-particle
;; 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-particle
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 particle 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 particle 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-particle [
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)) ]
]
;; PHASE 5: final updates
;; now recolor, since color is based on quantities that may have changed
recolor
ask other-particle
[ recolor ]
end
to recolor ;; particle procedure
ifelse speed < (0.5 * 10)
[
set color blue
]
[
ifelse speed > (1.5 * 10)
[ set color red ]
[ set color green ]
]
end
;;;
;;; drawing procedures
;;;
;; creates initial particles
to make-particles
create-particles number-of-particles
[
setup-particle
random-position
recolor
]
calculate-tick-delta
end
to setup-particle ;; particle procedure
set speed init-particle-speed
set mass particle-mass
set energy (0.5 * mass * (speed ^ 2))
set last-collision nobody
end
;; place particle at random location inside the box.
to random-position ;; particle procedure
setxy ((1 + min-pxcor) + random-float ((2 * max-pxcor) - 2))
((1 + min-pycor) + random-float ((2 * max-pycor) - 2))
end
to-report last-n [n the-list]
ifelse n >= length the-list
[ report the-list ]
[ report last-n n butfirst the-list ]
end
;; histogram procedure
to draw-vert-line [ xval ]
plotxy xval plot-y-min
plot-pen-down
plotxy xval plot-y-max
plot-pen-up
end
; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.
</pre>
</body>
</html>