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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)
  • Reply-to: hanlonr at cox.net

For difference equations use RSolve

In[1]:= 

Clear[y];

In[2]:= 

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

Out[2]= 

2 - 2^(1 - t)

In[3]:= 

{y[0], y[1]}

Out[3]=

 {0,1}

In[4]:= 

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.

Thanks in advance.




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