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MathGroup Archive 2007

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Re: NDSolve doesn't stop

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74333] Re: NDSolve doesn't stop
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 19 Mar 2007 01:58:52 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <etikd4$j5c$1@smc.vnet.net>

bar at ANTYSPAM.ap.krakow.pl wrote:
> I have a problem with PDE solving using NDSolve
> 
> tmax is  the stop time
> When I put tmax=21 NDSolve works very quickly (less than 1s)
> When I put tmax=22 NDSolve never ends without any error/warning
> 
> notebook file is "not readable" so I put it on www
> 
> http://robox.ap.krakow.pl/~bar/pde.nb
> 
> (file is less than 10kB)
> 
> Could Someone help me ?
> Regards Olaf
> 

tmax = 20 ==> no warning message issued (indeed for any 0 < tmax <)
=========

{{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 
options. More...

{{ET -> InterpolatingFunction[{{0., 21.}, {0., 1.}}, <>], FI -> \
InterpolatingFunction[{{0., 21.}, {0., 1.}}, <>]}}


tmax = 22 ==> things are going awry
=========

[aborted]

tmax = 23 ==> a warning message is issued: it might be worth reading it
=========

  NDSolve::"eerr" : "Warning: Scaled local spatial error estimate of 
(12.594134737787265) at (t) = (23.) 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 
options. More...

{{ET -> InterpolatingFunction[{{0., 23.}, {0., 1.}}, <>], FI -> \
InterpolatingFunction[{{0., 23.}, {0., 1.}}, <>]}}


tmax = 24 ==> no warning message issued
=========

{{ET -> InterpolatingFunction[{{0., 24.}, {0., 1.}}, <>], FI -> \
InterpolatingFunction[{{0., 24.}, {0., 1.}}, <>]}}

Regards,
Jean-Marc


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