modelling biological & physical systems Simon Lynch s.c.lynch@tees.ac.uk

biological systems simple (eg: cell growth) swarming & flocking evolution ecosystems

physical systems examples... atomic (sub-molecular) small & fast molecular (fluid particles, etc) erosion big & slow continental movement weather systems lots to climate change model

moths, fires, etc

the problem complexity #1 – scale spatial - too big or too small temporal - too fast or too slow logical - too many objects / parts

the problem complexity #2 – interactivity lots of interaction between parts lots of interdependence between parts emergent behaviour eg: cellular automata

computational modelling spreadsheets, etc? ok for some v.simple systems but – no observation programming languages ok but – big effort needed (& lots of time) special modelling tools eg: NetLogo (ccl.northwestern.edu/netlogo/) good & quick but some limitations

sample NetLogo code from NetLogo sample model library "Moths" model to move-thru-field ;; turtle procedure ifelse (light-level <= ( 1 / (10 * sensitivity) )) [ ;; if there is no detectable light move randomly rt flutter-amount 45 ] [ ifelse (random 25 = 0) ;; add some additional randomness to movement [ rt flutter-amount 60 ] [ ;; turn toward the brightest light maximize ;; if light ahead below sensitivity threshold ;; head to it otherwise move randomly ifelse ( [light-level] of patch-ahead 1 / light-level > ( 1 + 1 / (10 * sensitivity) ) ) [ lt ( direction * turn-angle ) ] [ rt flutter-amount 60 ] ]] if not can-move? 1 [ maximize ] fd 1 end from NetLogo sample model library "Moths" model