Re: Bug in SymbolicSum, or am I just stupid?
- To: mathgroup at smc.vnet.net
- Subject: [mg5637] Re: [mg5593] Bug in SymbolicSum, or am I just stupid?
- From: Dave Snead <dsnead at pacbell.net>
- Date: Wed, 1 Jan 1997 21:05:01 -0500
- Organization: Saguaro Software
- Sender: owner-wri-mathgroup at wolfram.com
Sean Luke wrote: > > I'm wondering if I'm just doing something really dumb, or if there > is some profound reason why Mathematica 2.2 seems to be finding different > symbolic infinite sumations for the same expression: > > Mathematica 2.2 for SPARC > Copyright 1988-94 Wolfram Research, Inc. > -- Terminal graphics initialized -- > > In[1]:= <<Algebra`SymbolicSum` > > In[2]:= ?SymbolicSum > SymbolicSum[f, {i, imin, imax}] attempts to find the value of Sum[f, {i, imin, > imax} ] for symbolic imin,imax. SymbolicSum[f, {i, imax}] evaluates the sum > of f with i running from 1 to imax. > > In[2]:= Simplify[(2)( 1/(2^n ) - ((n+1)/2)(1/(2^n))] (* expression 1 *) > > 3 - n > Out[2]= ----- > n > 2 2 > > In[3]:= Simplify[(2 - (n+1)/2) (1/(2^n))] (* expression 2--should be same *) > > 3 - n > Out[3]= ----- > n > 2 2 > > In[4]:= SymbolicSum[(2)( 1/(2^n) ) - ((n+1)/2)(1/(2^n)),{n,1,Infinity}] (*1*) > > 1 > Out[4]= - > 2 > > In[5]:= SymbolicSum[(2 - (n+1)/2) (1/(2^n)),{n,1,Infinity}] (*2*) > > 3 > Out[5]= -(-) > 4 > > In[6]:= SymbolicSum[Out[3],{n,1,Infinity}] (* simplified *) > > 3 > Out[6]= -(-) > 4 > > Thanks very much anyone. Sorry if this is a FAQ or obnoxious newbie question. > > Sean Luke > U Maryland at College Park, very late a night > seanl at cs.umd.edu This looks like a bug in 2.2: Mathematica 2.23 under Windows 95 gives In[1]:= <<Algebra`SymbolicSum` In[2]:= SymbolicSum[(3-n)/2^(n+1),{n,1,Infinity}] 3 Out[2]= -(-) 4 while Mathematica 3.0 (which has apparently incorporated the SymbolicSum functionality into Sum) gives In[1]:= Sum[(3-n)/2^(n+1),{n,1,Infinity}] 1 Out[1]= - 2 which is clearly the correct answer Dave Snead dsnead at pacbell.net