Presentation on theme: "1/32 StarLogo Andrew Begel University of California, Berkeley Agent Simulation Workshop October 16, 1999 Building a Modeling Construction Kit for Kids."— Presentation transcript:
1/32 StarLogo Andrew Begel University of California, Berkeley Agent Simulation Workshop October 16, 1999 Building a Modeling Construction Kit for Kids The StarLogo Team at MIT: Prof. Mitchel Resnick Brian Silverman Andrew Begel Bill Thies Vanessa Colella
2/32 Big Ideas StarLogo: a programmable modeling environment Intended for non-expert users and non- programmers –Great for kids, great for researchers! Emphasis on decentralized behaviors with local interactions.
3/32 Talk Outline History of StarLogo Models of Parallelism Parallel Communication Parallel Debugging StarLogo Workshop StarLogo for Java
4/32 History 1990s:*Logo on the Connection Machine 2 (a massively parallel computer) 1994: MacStarLogo on 68K and PPC Macs 1999: StarLogo in Java
5/32 Logo Developed by Feurzeig and Papert in 60s Based on Lisp –simpler syntax –incorporates elements of natural language. Interactive programming environment
6/32 Turtle Logo Turtle can move around a grid-based world. The turtle is an object to think with. –body syntonics Example Code: to square pendown repeat 4 [forward 10 right 90] end
7/32 StarLogo Thousands of turtles instead of just one ( can be organized in groups called breeds). Background grid of patches can run Logo code. The user is the observer and can discover and modify global characteristics of the model.
10/32 Simulating Parallelism How do you simulate parallelism on a computer with one processor? Our goal is realistic looking parallelism. –Preemptive multi-threading Switch threads every n milliseconds. –Cooperative multi-threading Switch threads at carefully chosen program points. Fine-granularity vs. coarse granularity We context switch after each command, but not each reporter.
12/32 time 12435 All jobs are scheduled in parallel. Commands are switched one after another. Jobs may get out of sync. StarLogo for Java Parallelism Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #2 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #2 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #2 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #2 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #2 Cmd #1 Cmd #2 Cmd #3 Cmd #4 Cmd #5 Cmd #1
13/32 Patch Parallelism CM2: –All patches execute the same code in lockstep. Mac: –Each patch runs through the code one by one. –Context switch after each patch has finished. Java: –Patches may no longer run code.
14/32 Observer Execution Theres only one observer. Its like a lifeguard sitting in a high chair at (0, 0). May view and modify global characteristics of the model. –Create turtles. –Gather statistics about turtles and patches. Performs various auxiliary functions: –Plotting, Movies, File I/O, Data Collection
15/32 Putting It All Together In MacStarLogo, how do we run the turtles, patches and observer? Forever buttons: In a loop, 1.Run turtles as many times as you can for 1/60th of a second 2.Run patches once 3.Run one observer forever button Command Center and Buttons: Observer code interrupts loop. Turtle or patch commands are run after forever button code have finished running once. Only one command center function may be running at any time.
16/32 Putting It All Together (2) In StarLogo for Java: All jobs are scheduled in a round-robin queue. Each job has equal priority. Forever buttons are the same as normal buttons, but the code has a loop [ button-code ] around it. Monitors spawn jobs, too. –While anything is running, monitors are run in a loop with a wait delay at the end. –When everything stops, monitors are run once more to show current values.
17/32 Model Timing How do you relate real time (in seconds, minutes, hours, days or years) to model time (in observer/turtle commands)? Answer: Its not easy. –StarLogo is qualitative, not quantitative. –One idea: Use the observer to time how long the turtles take to finish one cycle.
18/32 Parallel Communication Goal: Turtles must communicate with each other. –Message passing –Action at a distance How can we do it? 1. Set a global variable 2. Set a patch variable 3. Set a turtle variable
19/32 Visible from anywhere in the world. Theres only one copy, so it better not change quickly (else only monotonically) in order that all turtles have a chance to see it. Example (next slide). Communicating Through Globals
20/32 globals [season [fall winter spring summer]] to go every 10 [change-seasons] end to change-seasons case season [fall [set season winter] winter [set season spring] spring [set season summer] summer [set season fall]] end to grow-grass case season [spring [repeat 100 [plant-grass]] summer [repeat 85 [plant-grass]] fall [turn-all-grass-brown] winter [kill-all-grass]] end
21/32 Communicating Through Patches Only visible on that patch Useful for communicating information to all turtles on that location (i.e. infection) Example (next slide)
22/32 patches-own [sick-here?] turtles-own [sick?] to infect ifelse sick? [set sick-here? true] ;; Im sick. [if sick-here? [set sick? true]] ;; healthy wiggle end to wiggle right random 100 left random 100 if sick? and count-turtles-here-with [sick?] = 1 [set sick-here? false] forward 1 end
23/32 Communication via Turtles Directly read and modify other turtles variables. turtles-own [dead?] to kill :turtle-id set dead?-of :turtle-id true end to check-if-dead if dead? [die] end
24/32 Turtle-Turtle Communication Issues Must be able to find a turtle to talk to it. –one-of-turtles-here, one-of-frogs, one-of-turtles-with [color = red] Must remember its name to talk to it more than once. –i.e. one-of-turtles-here changes over time. –Other turtles never stop moving. Communication is asymmetric. –Just because turtle #1 talks to turtle #2 doesnt mean that turtle #2 talks to turtle #1.
27/32 Grab! StarLogo for Java breeds [girls guys] turtles-own [mygene child-gene father-color] to procreate if breed = girls [grab one-of-guys-here [set father-color color-of partner set child-gene combine mygene mygene-of partner hatch [ifelse (random 2) = 0 [set breed guys] [set breed girls] set mygene child-gene set color father-color]]] end
28/32 Parallel Debugging In MacStarLogo, with 2000 turtles, how do you figure out if something went wrong? Stack overflow (too many nested functions) and divide by zero in turtles and patches are ignored. Unexpected behaviors due to not knowing how the compiler interpreted your code. Look at turtle or patch state: –Oops, no print capability for turtles or patches. –Use turtle monitors to view all variables for a turtle. –Use command center to ask turtles or patches to set observer variables (or set turtle variables that are visible from the turtle monitor).
29/32 Parallel Debugging (2) Java StarLogo oSimpler programming model (separate turtle and observer procedures) to eliminate certain kinds of programming bugs. –Turtles and observer can use print (output shows up in the appropriate command center). –Runtime errors in turtles and observer pop up in a dialog box. (What happens if all 2000 turtles have the error? 2000 dialog boxes?) –Much better compiler error messages. They even report the line number of the error! –Turtle monitors and patch monitors will be added soon.
30/32 StarLogo for Java: New Features Works on PC, Mac and Unix! Rectangular (non-square) patch grid. Turtles and observer can play sounds. ( count, one-of, list-of )-( turtles, breeds )-( here, at, towards ) reporters. 64-bit double math. Unlimited number of turtles and number of variables. All math and list operations work for both turtles and observer. New primitives: case, let, loop, wait-until, random- gaussian, pick, kill, nmin, nmin4, nmax, nmax4, diffuse4
31/32 Workshops Teacher and student workshops held at Santa Fe Institute in Summer 99. –Learning through Adaptive Agent Computer Models (Pictures: http://www.taumoda.com/web/sfi99/) –Run by Vanessa Colella, Eric Klopfer and Monica Linden from MIT, Larry Latour from U. Maine, and Nigel Snoad from SFI –Project Building (StarLogo Workbook Challenges) –Group Activities (StarPeople) –Predator/Prey Badge Activity
32/32 Whats next? Jan 2000: Finish StarLogo for Java 1.0 –Plotting, Shapes, Paint Tools, Turtle and Patch Monitors, Output and Information Windows –StarLogo Project Web Player –GIS Support Finish StarLogo Workbook For more information: http://www.media.mit.edu/starlogo