Re: A question about summation indicies

*To*: mathgroup at smc.vnet.net*Subject*: [mg33112] Re: [mg33095] A question about summation indicies*From*: "Mark Morrissey" <mmorriss at ou.edu>*Date*: Sun, 3 Mar 2002 06:30:40 -0500 (EST)*References*: <200203011153.GAA27884@smc.vnet.net> <007a01c1c18f$ef645a60$e2b9eb94@dqb2301>*Sender*: owner-wri-mathgroup at wolfram.com

Thank you very much Tomas - I looked at FullForm after I sent the message and saw the underlying form was the reason (i.e. tehy're different). What I am trying (naively) to do is to derive through mathematica an equation for the standard error of a raingauge network I put together about 10 years ago. I'm finding that I have to learn more to do things algebracially. I'm still struggling with why you have to define x first. I'll do some more experimenting. Thanks - Mark Mark Morrissey Associate Professor of Meteorology Associate State Climatologist for Research University of Oklahoma 710 Asp Ave, Suite 8 Norman, OK 73069 405 447-8412 ----- Original Message ----- From: "Tomas Garza" <tgarza01 at prodigy.net.mx> To: mathgroup at smc.vnet.net Subject: [mg33112] Re: [mg33095] A question about summation indicies > Yes, it does. x has not ben defined, so let's take a look at what's going on > using FullForm (BTW, try not use capital letters for your variables; they > are supposed to be reserved for Mathematica functions): > > In[1]:= > FullForm[Sum[x[i], {i, 1, n}]] > Out[1]//FullForm= > Sum[x[i], List[i,1,n]] > > Something similar happens for the Sum with j instead of i, and it is obvious > that List[i, 1, n] is not equal to List[j, 1, n], and this is why you don't > get a "True". However, if you have a previously defined x, for example > > In[2]:= > x[i_] := 2^i > > then > > In[3]:= > Sum[x[i], {i, 1, n}] == Sum[x[j], {j, 1, n}] > Out[3]= > True > > Tomas Garza > Mexico City > > ----- Original Message ----- > From: "Mark Morrissey" <mmorriss at ou.edu> To: mathgroup at smc.vnet.net > Sent: Friday, March 01, 2002 5:53 AM > Subject: [mg33112] [mg33095] A question about summation indicies > > > > Hi - I have a simple question that probably has a simply answer. > > > > Why does Sum[x[i],{i,1,N}]==Sum[x[j],{j,1,N}] > > > > not produce a 'True' in Mathematica??? > > > > > > Mark Morrissey > > Associate Professor of Meteorology > > Associate State Climatologist for Research > > University of Oklahoma > > 710 Asp Ave, Suite 8 > > Norman, OK 73069 > > 405 447-8412 > > > > > > > > >

**References**:**A question about summation indicies***From:*"Mark Morrissey" <mmorriss@ou.edu>

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