Re: Unrelated variable affects rsolve result

*To*: mathgroup at smc.vnet.net*Subject*: [mg124690] Re: Unrelated variable affects rsolve result*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Tue, 31 Jan 2012 05:40:20 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201201301011.FAA17638@smc.vnet.net>

Evaluate ?? K K is a default generic name for a summation index in a symbolic sum. Hence the often repeated rule: To avoid naming conflicts with existing or future internal Mathematica variable names, never start a user-defined variable name with a capital letter. Bob Hanlon On Mon, Jan 30, 2012 at 5:11 AM, Nils Kanning <nils at kanning.de> wrote: > 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 >

**References**:**Unrelated variable affects rsolve result***From:*Nils Kanning <nils@kanning.de>