       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?  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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