NDSolve Repeated convergence test failure

*To*: mathgroup at smc.vnet.net*Subject*: [mg47092] NDSolve Repeated convergence test failure*From*: Steven Rey Ortiz <sro7516 at cs.tamu.edu>*Date*: Thu, 25 Mar 2004 05:48:23 -0500 (EST)*Organization*: Texas A&M University, College Station, Texas*Sender*: owner-wri-mathgroup at wolfram.com

Howdy! I at trying to use NDSolve to evaluate a set of three ODEs (two second order and one first order). However, by construction the third function value will eventually eliminate the second order terms of the other two equations, and when it does this, Mathematica returns a "Repeated convergence test failure" and stops evaluating. Is there a way to continue the integration process beyond this point? The differential equations are still meaningful. Following is a link to the notebook with the specific equations. The last line shows the error. http://students.cs.tamu.edu/sro7516/double-pendulum.nb Problem Background: I am experimenting with an adaptive controller for a double pendulum system. The notebook first defines the equations of motion for the system. The controller assumes an initial value for the mass of the second link, but adjusts this value based on feedback from the system. When it has the correct value for the mass, the control law will cancel the secend order terms from the equations of motion (and correctly track the desired trajectory). Any suggestions or ideas you have to overcome this NDSolve problem would be most welcome! Thanks! Steve Ortiz