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MathGroup Archive 2000

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Re: Question: numerical solution of nonlinear differential equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg26403] Re: [mg26390] Question: numerical solution of nonlinear differential equation
  • From: "Carl K. Woll" <carlw at u.washington.edu>
  • Date: Wed, 20 Dec 2000 00:21:29 -0500 (EST)
  • References: <200012160740.CAA05212@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Ronald,

I tried out your problem and it seems to work for some random values of the
constants.

In[8]:=
NDSolve[{2 y''[x] + 3 y'[x] + 4 Exp[-5 x]==0, y'[0]==0, y'[1]==0},y,{x,0,1}]

produces an error message about RowReduce, but it also produces an answer. A
problem with the input in your post is that you had y[x]' instead of y'[x].
Also, it is not wise to use capital letters as arbitrary constants, as many
of them have a special meaning in Mathematica. For example, D is the
differentiation function, and E=2.7818... is the exponential constant e.

You should also realize that Mathematica's NDSolve can only solve a single
linear boundary value ODE.

Carl Woll
Physics Dept
U of Washington


----- Original Message -----
From: "Ronald Sastrawan" <sastra at fmf.uni-freiburg.de>
To: mathgroup at smc.vnet.net
Subject: [mg26403] [mg26390] Question: numerical solution of nonlinear differential
equation


>
> Hello !
>
> I encountered a problem, trying to numerically solve a differential
> equation.
> My equation looks like:
>
> A y''[x] - B y[x]' + C Exp[-Dx] == 0
> with boundary conditions: y'[0]==0 , y'[E]==0
>
> All constants A to E are known.
>
> Mathematica complains, that the equation is not linear. But in the
> online documentation I saw many examples of nonlinear differential
> equations, which all work fine. What is the difference between the
> examples and my equation ? And is there a possibility to NDSolve my
> equation ?
>
> Any hint on this would be of great help to me.
>
> Thanks a lot,
>
> Ronald
>
> --
> Ronald Sastrawan
>
> Freiburg Materials Research Center
> Stefan-Meier-Str. 21
> D-79104 Freiburg
> Germany
> Tel: ++49/761/203-4802
> FAX: ++49/761/203-4801
> EMAIL: sastra at fmf.uni-freiburg.de
> http://www.fmf.uni-freiburg.de/~biomed/FSZ/forschung-FSZ.html
>
>
>



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