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Re: How to pass initial conditions to IDA methods via NDSolve?

• To: mathgroup at smc.vnet.net
• Subject: [mg121841] Re: How to pass initial conditions to IDA methods via NDSolve?
• From: Oliver Ruebenkoenig <ruebenko at wolfram.com>
• Date: Wed, 5 Oct 2011 03:57:51 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

Hi,

On Tue, 4 Oct 2011, GRW wrote:

> New to Mathematica so this might be gibberish.

Without seeing the equations this is hard to answer. What follows are some 
random ideas.
>
> I'm trying to integrate numerically a PDE system. NDSolve complains
> saying this:
>
> "NDSolve::icfail: Unable to find initial conditions that satisfy the
> residual function within specified tolerances. Try giving initial
> conditions for both values and derivatives of the functions."
>
> Now I've figured out how to get numerical estimates for some of the
> derivatives in my PDE system (using FindRoot there).
> However, if I add these conditions to my preexisting list of initial
> conditions and boundary conditions, Mathematica complains that there
> are too many boundary and/or initial conditions:
>

- Try lowering AccuracyGoal/PrecisionGoal
- Can you use exact values for your equations?


> "NDSolve::ivone: Boundary values may only be specified for one
> independent variable. Initial values may only be specified at one
> value of the other independent variable"
>

In the time integration method option, try giving "Timevariable" -> t

> It seems as if IDA was selected automatically as "Method" option of
> NDSolve and IDA does not seem to allow for initial conditions passed
> to it.

There is information about the IDA here:

tutorial/NDSolveIDAMethod

Hope this gets you started.

Oliver

>
> I've tried using Method option "Shooting" (because this one seems to
> allow for initial conditions passed), however NDSolve isn't too fond
> of that one either:
> "NDSolve::nodae: The method NDSolve`Shooting is not currently
> implemented to solve differential-algebraic equations. Use Method ->
> Automatic instead."
>
>
> Any advice greatly appreciated!
>
>