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MathGroup Archive 1997

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Re: solve this equation?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7304] Re: solve this equation?
  • From: Eugene Lee <elee at aw.sgi.com>
  • Date: Fri, 23 May 1997 01:41:33 -0400 (EDT)
  • Organization: Alias Wavefront
  • Sender: owner-wri-mathgroup at wolfram.com

Wilson Figueroa wrote:
> 
> 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.


There is no problem with my solution. Ask any mathematician if you don't see.

Eugene Lee


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