BehaviorSpace freezes on step #0 - netlogo

Question

Sorry if this is obvious, I have searched everything I can think of and asked a colleague and we are both stuck.
I have some code (below - a slight twist on wolf sheep predation) that I want to run behaviorspace (input also below). However, it never runs to completion. It always seems to get stuck on step #0 of a run (the run # it gets stuck on varies). The runs that it sticks on work fine if they are run in isolation (so all the variables seem fine). It just seems to freeze (producing no error messages, nor does it crash).
Any ideas what is causing it?
Thanks,
Simon
Code:
globals [grass] ;; keep track of how much grass there is
;; Sheep and wolves are both breeds of turtle.
breed [sheep a-sheep] ;; sheep is its own plural, so we use "a-sheep" as the singular.
breed [wolves wolf]
turtles-own [energy] ;; both wolves and sheep have energy
patches-own [countdown]
to setup
clear-all
ask patches [ set pcolor green ]
;; check GRASS? switch.
;; if it is true, then grass grows and the sheep eat it
;; if it false, then the sheep don't need to eat
if grass? [
ask patches [
set countdown random grass-regrowth-time ;; initialize grass grow clocks randomly
set pcolor one-of [green brown]
]
]
if fences?[ ; this code adds in blue fences to create patches of various size (if fences are turned on). Turtles cannot pass over fences
ask patches with [pxcor mod connectivity2 = 0]
[ set pcolor blue ]
ask patches with [pycor mod connectivity = 0]
[ set pcolor blue ]
]
set-default-shape sheep "sheep"
create-sheep ((count patches - (count patches with [pcolor = blue])) / 25) ;; create the sheep, then initialize their variables. The starting density always remains constant despite a varying world size
[
set color white
set size 1.5 ;; easier to see
set label-color blue - 2
set energy random (2 * sheep-gain-from-food)
setxy random-xcor random-ycor
]
set-default-shape wolves "wolf"
create-wolves ((count patches - (count patches with [pcolor = blue])) / 50) ;; create the wolves, then initialize their variables. The starting density always remains constant despite a varying world size
[
set color black
set size 2 ;; easier to see
set energy random (2 * wolf-gain-from-food)
setxy random-xcor random-ycor
]
display-labels
set grass count patches with [pcolor = green]
reset-ticks
end
to go
if count wolves = 0 and count sheep = 0 and ((count patches with [pcolor = green]) = (count patches - (count patches with [pcolor = blue]))) [ stop ] ; stop model when the whole world has flipped to grass
ask sheep [
move
if grass? [
set energy energy - 1 ;; deduct energy for sheep only if grass? switch is on
eat-grass
]
death
reproduce-sheep
]
ask wolves [
move
set energy energy - 1 ;; wolves lose energy as they move
catch-sheep
death
reproduce-wolves
]
if grass? [ ask patches [ grow-grass ] ]
set grass count patches with [pcolor = green]
tick
display-labels
end
to move ;; turtle procedure
rt random 50
lt random 50
ifelse [pcolor] of patch-ahead 1 = blue
[ move] ;; If there is a blue patch ahead of you, choose another random direction
[ fd 1 ] ;; Otherwise, it is safe to move forward.
end
to eat-grass ;; sheep procedure
;; sheep eat grass, turn the patch brown
if pcolor = green [
set pcolor brown
set energy energy + sheep-gain-from-food ;; sheep gain energy by eating
]
end
to reproduce-sheep ;; sheep procedure
if random-float 100 < sheep-reproduce [ ;; throw "dice" to see if you will reproduce
set energy (energy / 2) ;; divide energy between parent and offspring
hatch 1 [ ifelse [pcolor] of patch-ahead 1 = blue ;; hatch an offspring
[ move] ;; If there is a blue patch ahead of the offspring, it chooses another random direction
[ fd 1 ] ;;If not, offspring move forward 1 step
]]
end
to reproduce-wolves ;; wolf procedure
if random-float 100 < wolf-reproduce [ ;; throw "dice" to see if you will reproduce
set energy (energy / 2) ;; divide energy between parent and offspring
hatch 1 [ ifelse [pcolor] of patch-ahead 1 = blue ;; hatch an offspring
[ move ] ;; If there is a blue patch ahead of the offspring, it chooses another random direction
[ fd 1 ] ;;If not, offspring move forward 1 step
] ]
end
to catch-sheep ;; wolf procedure
let prey one-of sheep-here ;; grab a random sheep
if prey != nobody ;; did we get one? if so,
[ ask prey [ die ] ;; kill it
set energy energy + wolf-gain-from-food ] ;; get energy from eating
end
to death ;; turtle procedure
;; when energy dips below zero, die
if energy < 0 [ die ]
end
to grow-grass ;; patch procedure
;; countdown on brown patches: if reach 0, grow some grass
if pcolor = brown [
ifelse countdown <= 0
[ set pcolor green
set countdown grass-regrowth-time ]
[ set countdown countdown - 1 ]
]
end
to display-labels
ask turtles [ set label "" ]
if show-energy? [
ask wolves [ set label round energy ]
if grass? [ ask sheep [ set label round energy ] ]
]
end
; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.
behaviorspace input:
variables:
["world-width" 51]
["fences?" true]
["wolf-gain-from-food" 20]
["sheep-reproduce" 7]
["show-energy?" false]
["grass?" true]
["connectivity" 10 25 50]
["wolf-reproduce" 5]
["grass-regrowth-time" [1 1 100]]
["sheep-gain-from-food" 4]
repetitions: 1
reporters:
count wolves
count sheep
count patches with [pcolor = green]
measure runs at each step
setup: setup
Go: go
Stop (I have tried it with and without this): count wolves = 0 and count sheep = 0 and ((count patches with [pcolor = green]) = (count patches - (count patches with [pcolor = blue])))
Time limit: 5000

Answer 1

It's difficult for me to imagine this could be caused by anything other than running low on memory. Running very low on memory can cause the JVM to slow to a crawl.
What do the memory usage stats in the System tab of "About NetLogo" say? You can verify there that you're actually getting the heap size you asked for.