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MathGroup Archive 1999

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Bug in RSolve?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18897] Bug in RSolve?
  • From: "Hossein Kazemi" <kazemi at som.umass.edu>
  • Date: Mon, 26 Jul 1999 14:27:43 -0400
  • Organization: University of Massachusetts, Amherst
  • Sender: owner-wri-mathgroup at wolfram.com

Is this a bug in RSolve (Version 4.0)?

In[1]:=
<< DiscreteMath`RSolve`

In[2]:=
RSolve[x[n] == 3 + 4 u[n], x[n], n];

In[3]:=
x[n_] = x[n] /. %[[1]];

In[4]:=
x[1]

Out[4]=
3 - 4 u[-1] + 4 u[1]           What does u[-1] doing here?

In[5]:=
x[2]

Out[5]=
3 - 4 u[-1] + 4 u[2]           What does u[-1] doing here?

In[6]:=
u[n_] := n

In[7]:=
x[2]

Out[7]=
15

This does not make any sense at all.  Clearly,

x[2]= 3 + 4*2 = 11





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