Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Graphing Difference Equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91407] Re: Graphing Difference Equation
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 20 Aug 2008 06:22:39 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <g8gj3h$eso$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

a) you have serious problems with the Mathematica syntax
    the equation
       y_{t} = 1.5y_{t-1} - .5y_{t-2} = 0
    is total nonsense because you have either

    y[t] == 3*y[t - 1]/2 - y[t - 2]/2

    or
     3*y[t - 1]/2 - y[t - 2]/2==0
   or y[t]==0
b) If you have a discrete equation you must plot
    discrete values and not a continuous function,
    i.e.

sol = y[t] /. RSolve[y[t] == 3*y[t - 1]/2 - y[t - 2]/2, y[t], t][[1]];

ListPlot[Table[Evaluate[sol /. {C[1] -> 1 , C[2] -> 0}], {t, 0, 10}]]

Regards
   Jens


Walkman 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.
> 


  • Prev by Date: Re: LaTex to Mathematica
  • Next by Date: Re: LaTex to Mathematica
  • Previous by thread: Graphing Difference Equation
  • Next by thread: Re: Graphing Difference Equation