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

**Follow-Ups**:**Re: Unrelated variable affects rsolve result***From:*Bob Hanlon <hanlonr357@gmail.com>