       Re: Graphing Difference Equation

• To: mathgroup at smc.vnet.net
• Subject: [mg91426] Re: [mg91393] Graphing Difference Equation
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Thu, 21 Aug 2008 04:15:53 -0400 (EDT)

```For difference equations use RSolve

In:=

Clear[y];

In:=

y[t_] = y[t] /.
RSolve[{
y[t] == (3*y[t - 1] - y[t - 2])/2,
y == 0, y == 1},
y[t], t][] //
Simplify

Out=

2 - 2^(1 - t)

In:=

{y, y}

Out=

{0,1}

In:=

Plot[y[t], {t, 0, 20}, PlotRange -> All]

Bob Hanlon

---- Walkman <uvnarae at hotmail.com> wrote:

=============
Dear Group.

I have a trouble in graphing differece equation using mathematica.

For instance, I get a difference equation,

y_{t} = 1.5y_{t-1} - .5y_{t-2} = 0

Since I don't know how to input the code for graphics and just want

to check how the graph looks like,

I input the solution instead, A(-1.2)^t + B(.5)^t where A and B

constants

For simplicity, I choose A = B = 1.

Plot[(-1.2)^t + (.5)^t,{t,0,20}]

The problem is that it doesn't work at all.

If anyone who know exact way to graph difference equation, plz

tell me.