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Unrelated variable affects rsolve result

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124671] Unrelated variable affects rsolve result
  • From: Nils Kanning <nils at kanning.de>
  • Date: Mon, 30 Jan 2012 05:11:32 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

Hello,
I am using Mathematica 8.0.1.0 and I observed a strange behavior of the
function rsolve. The result rsolve produces is changed by a seemingly
unrelated variable, which I define before calling rsolve. Especially
rsolve seems to interfere with a variable called "K", whereas other
variables (for example "k") do not cause problems.

Here is some code, which illustrates this behavior:

In[1]:= k = {{1, 0}};
In[2]:= RSolve[ h[y] == 1 + h[y + 1], h[y], y]
Out[2]= {{h[y] -> -y + C[1]}}
In[3]:= K = {{1, 0}};
In[4]:= RSolve[ h[y] == 1 + h[y + 1], h[y], y]
During evaluation of In[4]:= Sum::write: Tag List in {{1,0}}[1] is
Protected. >>
Out[4]= {{h[y] -> C[1] + \!\(
\*UnderoverscriptBox[\(\[Sum]\), \({{1, 0}}[1] = 0\), \(\(-1\) +
       y\)]\(-1\)\)}}

Is there a special meaning of "K" or does this variable just interfere
with some internals of rsolve?

Thanks,
Nils



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