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Re: StoppingTest does not work ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg9825] Re: [mg9769] StoppingTest does not work ?
  • From: Wouter Meeussen <vdmcc at vandemoortele.be>
  • Date: Fri, 28 Nov 1997 05:35:39 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Cher Gilles,


the following works:

In[30]:=sol1=NDSolve[{y'[t]==y[t],y[0]==1},{y},{t,0,2}] Out[30]={{y ->
InterpolatingFunction[{{0., 2.}}, <>]}}
In[33]:=sol2=NDSolve[{y'[t]==y[t],y[0]==1},{y},{t,0,2},StoppingTest->(y[t]>3)]
Out[33]={{y -> InterpolatingFunction[{{0., 1.0988}}, <>]}}

In[32]:=y[1]/.sol1
Out[32]={2.71829}

In[40]:=y[1.0988]/.sol2
Out[40]={3.00057}


in for a picture ?
In[39]:=Plot[{y[x]/.sol1,y[x]/.sol2},{x,0,1.5},PlotStyle->{{Hue[0]},{Hue[.7]}}];

InterpolatingFunction::dmval: 
   Input value {1.12545} lies outside the range of data in
     the interpolating function. Extrapolation will be used.

-- nice plot --


I guess your example {y'[t]==1,y[0]==0} is partly "bonkers" (?) it
should come out y->t of course.

A propos:
Options[NDSolve] lists "StoppingTest", neither the manual nor online
help do!

according to standard notation, a "test" should be a (pure) function of
the thing to be tested, like (y[#]>1&), but it does not seem to be so
in this case.

hmmm, strange.


wouter.



At 12:07  25.11.97 -0500, Gilles BARBIER wrote:
>
>     Anyone could tell me why :
>     
>     NDSolve[{y'[t]==1,y[0]==0},{y},{t,0,2},StoppingTest->(y[t]>1)]
>     
>     does not stop for t=1 (it does not stop at all, in fact).
>     Of course, my problem is more complicated, but in all case 
>     stoppingTest seems to stop when it wants...
>     
>     Thanks for quick help, Please !!!
>     
>     Gilles.
>


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