negativ update rate in .world file

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Hi guys, what does a negativ update rate in a .world file mean? i was told that the simulation then runs as far as possible in order to provide nearly realtime simulation.But i cant find a documentation or explanation in ros or ODE. Is that true? Where can i find a documentation about that?? <physics:ode> <steptime>0.001</steptime> <gravity>0 0 -9.8</gravity> <cfm>0.0000000001</cfm> <erp>0.2</erp> <quickstep>true</quickstep> <quickstepiters>10</quickstepiters> <quickstepw>1.3</quickstepw> <contactmaxcorrectingvel>100.0</contactmaxcorrectingvel> <contactsurfacelayer>0.001</contactsurfacelayer> <updaterate>-0.1</updaterate> </physics:ode>