Using "EventLocator" with NDSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg126008] Using "EventLocator" with NDSolve*From*: Jason <jasonhsteffen at gmail.com>*Date*: Fri, 13 Apr 2012 04:43:40 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

I'm trying to use "EventLocator" to find the zeros of an ODE. Prior to doing so I generate the equations in the form y[1][t] == rhs y[2][t] == rhs etc. This format is suggested in the mathematica documentation (Generalizations & Extensions http://reference.wolfram.com/mathematica/ref/NDSolve.html) Unfortunately, for some reason I can't get the eventlocator method to work when the equations are written in this format. Below are three examples, the first two work, and the third (the above format) does not. I get the error message "The value of the event function at t = 0.0002... was not a real number. ..." NDSolve[{y''[t] + Sin[y[t]] == 0, y'[0] == 0, y[0] == 1}, y, {t, 0, 10}, Method -> {"EventLocator", "Event" -> y[t], "EventAction" :> Print[t]}]; NDSolve[{Subscript[y, 1]''[t] + Sin[Subscript[y, 1][t]] == 0, Subscript[y, 1]'[0] == 0, Subscript[y, 1][0] == 1}, Subscript[y, 1], {t, 0, 10}, Method -> {"EventLocator", "Event" -> Subscript[y, 1][t], "EventAction" :> Print[t]}]; NDSolve[{y[1]''[t] + Sin[y[1][t]] == 0, y[1]'[0] == 0, y[1][0] == 1}, y[1], {t, 0, 10}, Method -> {"EventLocator", "Event" -> y[1][t], "EventAction" :> Print[t]}]; Any suggestions?