```Date: Mar 7, 2013 10:48 PM
Author: W. Craig Carter
Subject: updating a simulation within Manipulate.

I *think* I've asked this question before, but I can't find it on mathgroup. In any case, I don't know the answer now.Here is a simple example of a Manipulate that updates a graphic as long as a boolean is true.  This method seems like a kludge to me---is it? If so, what would be a better way to do this.This is a constructed example, the real case I am looking at is much more involved; but kudos to anyone who can make a reasonable facsimile of their signature by adjusting the random walker's bias....randomStep[bias_, stepList_] := Module[{angle = RandomVariate[NormalDistribution[bias, 1]]},  Join[stepList, {Last[stepList] + {Cos[angle], Sin[angle]}}]]walkerGraphic[stepList_, range_] := Graphics[GraphicsComplex[stepList, Disk /@ Range[Length[stepList]]],  PlotRange -> range {{-1, 1}, {-1, 1}}]DynamicModule[ {walkerPath = {{0, 0}}}, Manipulate[  If[keepWalking,  (*  kludge warning---testing for If[True...] seems inefficient   *)   walkerPath = randomStep[bias, walkerPath]   ];  If[reset,   reset = False; keepWalking = False;   walkerPath = {{0, 0}}   ];  walkerGraphic[walkerPath, range],  {{keepWalking, False}, {True, False}},  {{reset, False}, {True, False}},  Delimiter,  {{range, 20}, 0, 100},  {{a, 0}, -Pi, Pi,   AngularGauge[##, ImageSize -> 160 ,     ScaleOrigin -> {{-4 Pi, 4 Pi}, 1}] &}  ] ]W Craig CarterProfessor of Materials Science, MIT
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