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. >