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MathGroup Archive 2007

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Re: NDSolve doesn't stop

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74380] Re: NDSolve doesn't stop
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 19 Mar 2007 21:58:37 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <etikd4$j5c$1@smc.vnet.net> <etlchi$nrv$1@smc.vnet.net> <etlqaq$rai$1@smc.vnet.net>

bar at ANTYSPAM.ap.krakow.pl wrote:
> Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com> wrote:
> 
>> {{ET -> InterpolatingFunction[{{0., 20.}, {0., 1.}}, <>], FI -> \
>> InterpolatingFunction[{{0., 20.}, {0., 1.}}, <>]}}
>> tmax = 21 ==> a warning message is issued: it might be worth reading it
>>   NDSolve::"eerr" : "Warning: Scaled local spatial error estimate of 
>> (159.0346060966196) at (t) = (21.) in the direction of independent 
>> variable (x) is much greater than prescribed error tolerance. Grid 
>> spacing with (15) points may be too large to achieve the desired 
>> accuracy or precision. A singularity may have formed or you may want to 
>> specify a smaller grid spacing using the MaxStepSize or MinPoints 
> 
> Success!, Bun i'm not suse how it works :-)
> When i put:
> PrecisionGoal ->10 (if need by)
> MaxStepSize->0.005
> MaxSteps->Infinity
> 
> I can obtain silution for a long time (t=100 is enough)
> My question is : Is there optimal procedure to change this parameters?
> 
> Pegards, Olaf
> 
> 

You have to experiment by yourself case by case. There is no magic 
receipt to find the optimal values. (These values depend on the 
integrand as well as on the values -- by default or set by the user -- 
of some of the other options.)

Regards,
Jean-Marc


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