Transcript Designing Spatially Explicit Agent

Caribou – Wolf Interactions
• http://www.youtube.com/watch?v=nK1J
OmMQ5Fc
Issues with Simulations
• Realistic Movement
– Moving toward desired areas
– Keep animals from getting “stuck”
• Validation
• Boundary conditions
– What happens at the edges?
• Disappear/die (need immigration as well)
• Reverse direction
• Wrap to the other side (not realistic)
• Model stability
• Model complexity/Performance
Moving Toward Desired Areas
• Use Distance Raster
– Desired area:
• Spawning ground, feeding grounds
– Destination is desired area
– Pixels with lower cost are closer to desired
area
– Animals move to adjacent pixels with lower
cost
Moving Through Networks
• Use polylines with network nodes
• Move in direction (or against) of polylines
• Need to make decisions at nodes
Getting “Stuck”
• Certain conditions arise and animals can
become stuck and just move back and
forth
– Add additional randomness
– Examine environmental layers for unrealistic
values
• Streams not flowing perfectly down hill
• Bays not connected with the ocean
Validation
• Run models over and over again
• Record locations, births, deaths, feeding
– Create probability surfaces
• Validate against existing datasets
– Are observations/measurements within the
predicted areas?
– Could use likelihood/AIC…
Model Stability
• Density dependence
– Most species struggle more when crowded
– Reduces food availability, increases disease
– Places a control the number of individuals
• Balancing birth rates and death rates
• Realistic lifecycles, predation rates
Model Complexity
• Typically there are lots of agents
• Need to keep the behaviors and
attributes simple
• The group behaviors are typically more
complex than expected from the
individuals
• Model a population
– Convert “groups” of individuals to
populations when they cluster
Monte Carlo-Markov Chain
• Markov Chain:
– A series of states of being that have
probabilities associated with transitions (i.e.
the state is not deterministic but has some
stochastic component).
Performance
• Select the right resolution for rasters
– High enough to be realistic
– Low enough for speed
– May have to just simulate a smaller area
than desired.
3D and Temporal
• Simulations are almost always
temporally based
• 3D is common but requires more
hardware/time
– Also requires special software and 3D data
Ecological Modeling
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Water, carbon, nutrient cycling
Trophic models
Population models
Predator/Prey
Disease
wsu.edu
Sustainable Fisheries
www.niwa.co.nz
Can operating rooms
in Second Life teach
real doctors?
- Discover
Sims
World of Warcraft
Tools
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NetLogo
HexSim
MASON Multi-Agent Simulation Toolkit
Repast
Programming!
– Python
– Java
• Books: “Agent-Based Models of
Geographical Systems”
Envision – Policy Simulation
Simulations
• Parameterization
– Based on mechanisms/theories
– Typically include random effects
– “Tweeked” to fit reality
• Validation
– Run over observed space and time
• Do simulated measures match observed?
– Run it over and over
• Observed fit into “Confidence interval”?
Simulations
• Startup:
– Either simulate a known situation
– Or, run until reaches an expected state
• Stability
– Populations tend to breed out of control or
die out over time
– Build in realistic limitations
NetLogo
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Environment for 2D simulations
Easy to program
OpenSource, free
Was a “kids” language
Now used for education, visualization,
simple simulations
• Can install outside “Program Files”
• Run NetLogo.exe
• See included Tutorials
NetLogo – Model Interface
NetLogo Design
• NetLogo is a world made up of:
– Turtles: The agents that move
– Patches: Agents that do not move (i.e.
grass, buildings, roads)
– Links: Connections between turtles
– Observer: Oversees the action
Ecological Modeling
• Combination of cellular automata and
individually based models:
Grid of cells
(raster)
Individuals
NetLogo - Code
HexSim
• Visit Hexsim.net to download
• Decompress the folder
• Can run “Hexsim.exe” from within the
folder without other installation
• See the “Examples” on the HexSim
website to get started
– The User’s Guide has good information on
how HexSim works
HexSim Basics
• Set the workspace:
– HexSim -> Set Workspace
– Select a “*.grid” file
• Double click on a scenario to “open”
– Adds a tab for that scenario
– “Scenario” menu items work on the currently
selected tab
• View spatial data:
– In the “Spatial Data” panel, open items
– Double-click on “-> 1” to show the data
HexSim Basics
• Select “Scenario -> Run Simulation”
• Save an XML file for the run
• Click “Start” in the window that is
displayed
• These examples are not yet
parameterized so you may need to
modify them to do something interesting
Comparison of Software
• http://en.wikipedia.org/wiki/Comparison_
of_agent-based_modeling_software
Simulation Modeling
• Plate tectonics:
– http://www.youtube.com/watch?v=ryrXAGY
1dmE
• Wolf simulation game
– https://www.youtube.com/watch?v=idr0Ayl56Q
Possible Simple Models
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Fire w/fire fighters
Zombies and humans
Reef fish
Wolves and elk
Invasive species (w/managers)