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

```

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