       Iterative solution difficulty

• To: mathgroup at smc.vnet.net
• Subject: [mg99942] Iterative solution difficulty
• From: James <jborrell at umd.edu>
• Date: Tue, 19 May 2009 07:17:00 -0400 (EDT)

```I am trying to solve a system of ODEs using NDSolve until a desired ending condition is reached, then the value at the final time x[tf-] is "linearly" related to the new initial conditions, x[tf+] and the ODEs are solved until the ending condition again and so on.

The following code is the numerical solution to the equation of motion of a simple pendulum.  Physically, the pendulum is released from horizontal and then stopped at the vertical and returned to horizontal and solved again.  I expect the output to look periodic, similar to a capacitor discharging.

ICx1 = Pi/2;
ICxprime1 = 0;

output = NDSolve[{x''[t] == -g/L Sin[x[t]], x == ICx1, x' == ICxprime1} /. {g ->9.8, L -> 1}, x, {t, 0, 10},Method -> {EventLocator, "Event" -> x[t] > 0,EventAction :> Throw[t1 = t; ics1 = x[t];,StopIntegration"]}]

x1 = x[t1] + Pi/2 /. output[]
x1p = x'[t1] + 5 /. output[]

```

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