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MathGroup Archive 1997

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Re: solve this equation?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7200] Re: solve this equation?
  • From: Wilson Figueroa <wfigueroa at GI.COM>
  • Date: Fri, 16 May 1997 02:30:30 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

There is a problem with your solution.

Check the basic math once more.



Eugene Lee <elee at aw.sgi.com> wrote in article
<5k6g77$5bf$1 at dragonfly.wolfram.com>...
> Hong-liang Xie wrote:
> > 
> > Can Mathematica be used to handle equations as follows:
> > 
> >          u[x]  = 0.5 u[x-1] + 0.5 u[x+1]
> >          u[ 4] = 1
> >          u[-4] = 0
> > 
> > and find result for, say, u[0]?  Note that transforming
> > the equation to
> > 
> >          2u[x+1] = u[x]  - u[x-1]
> > 
> > doesn't help since the initial conditions are given on
> > the points 4 and -4.
> > 
> > Any hint would be appreciated.  Thanks a lot!
> > 
> > Hong
> 
> You don't need Mathematica at all. The equation
>         u[x]  = 0.5 u[x-1] + 0.5 u[x+1]
> is satisfied by any linear function (ie, whose graph is a straight
> line). The boungary conditions then fix the line, giving the solution as
>         u[x]=(x+4)/8
> 
> By the way, your transformed equation is written incorrectly.



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