Garbage collection problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg51803] Garbage collection problem*From*: D Herring <dherring at at.uiuc.dot.edu>*Date*: Tue, 2 Nov 2004 02:06:06 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

To anyone who can help me, I've written a small simulator to model the system I'm studying. It works nicely. Now I'm wrapping that simulator in a set of Do[] loops to generate maps of its behavior. Unfortunately, long runs quickly fill my 512MB of RAM, even when dumping all my data to files as it is generated. After a good bit of debugging, I have isolated (at least half of of) the memory problem to my use of a StoppingTest inside NDSolve. Example: (* Setup *) eq={9.8*(0.99*Cos[qS[t]] + 0.01*Cos[qH[t] + qS[t]]) - 0.01*Sin[qH[t]]*qH'[t]*qS'[t] - 0.01*Sin[qH[t]]* qH'[t]*(qH'[t] + qS'[t]) + (0.001 + 0.01*Cos[qH[t]])* qH''[t] + (0.982 + 0.02*Cos[qH[t]])*qS''[t] == 0, 0.1*Cos[qH[t] + qS[t]] + 0.01*Sin[qH[t]]*qS'[t]^2 + 0.001*qH''[t] + (0.001 + 0.01*Cos[qH[t]])*qS''[t] == 0, qS[0] == 1.71, qS'[0] == -1.01, qH[0] == 2.84, qH'[0] == 1.1}; vars={qS[t], qH[t], qS'[t], qH'[t]}; test=qH[t] >= Pi && 2*Cos[qH[t]/2]*Cos[qH[t]/2 + qS[t]]*Sin[Pi/180] + Cos[Pi/180]*(Cos[qS[t]]*Sin[qH[t]] + (1 + Cos[qH[t]])* Sin[qS[t]]) < -0.01 && Cos[qH[t] + qS[t]]* Derivative[1][qH][t] + (Cos[qS[t]] + Cos[qH[t] + qS[t]])* Derivative[1][qS][t] < -0.01 || Abs[qH[t]] < Pi/6 || Sin[qS[t]] < 1/4; $HistoryLength=0; (* end *) (* example a *) Do[ soln=NDSolve[eq,vars,{t,0,2}][[1]]; , {20}]; MemoryInUse[] (* end *) (* example b *) Do[ soln=NDSolve[eq,vars,{t,0,2},StoppingTest->test][[1]]; , {20}]; MemoryInUse[] (* end *) To reproduce this, start a fresh kernel. Execute the setup code, and then repeatedly run example a or b. When I repeatedly run example a, MemoryInUse[] quickly converges to a constant value, as expected. However, each run of example b results in an increase in memory consumption. Why? How can I fix/avoid this behavior? I stripped out some other logic, but all I really want are a few numbers from the last several "soln"s of each run, to observe convergence properties. FWIW, I'm running on $Version=5.0 for Linux (November 18, 2003) Thanks, Daniel