Re: Help please: Summing a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg13509] Re: [mg13480] Help please: Summing a list*From*: Carl Woll <carlw at fermi.phys.washington.edu>*Date*: Fri, 31 Jul 1998 04:33:24 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Hi Rob, There are several problems with the statement > PP[[i]]:=Sum[P[[n]],{n,0,i}]; The first problem is the use of double brackets instead of single brackets. Using double brackets like you do above implies that PP is already an object like a list with elements. This is what causes the error message which Mathematica gives you. The second problem is that in a function definition you should use an argument with a pattern. That is, PP[i_] instead of PP[i]. Otherwise, your definition only takes action when the argument is the letter i. The final problem is that you probably don't want to have your sum go from 0 to i, since the zeroth part of an expression is the head. For example, if s = {1,2,3} then s[[0]] is List and not 1. So, putting the above together, you probably want the definition PP[i_] = Sum[ P[[n]], {n,1,i} ] Carl Woll Dept of Physics U of Washington On Sun, 26 Jul 1998 robpetersonSPAMME at iname.com wrote: > I make a list of numbers, eg: > > P=Table[6,{x,0,110}]; (I have a more interesting list to use later if I > get this working) > > Now I want to make another list PP in which each entry PP[[i]] is the > sum of P's first i entries. I try > > PP[[i]]:=Sum[P[[n]],{n,0,i}]; > > At the definition, I get the following error: Part::"pspec": > "Part specification \!\(n\) is neither an integer nor a list of > integers." > > I don't know how to make n an integer. In the definition of Sum[], it > seems n is an integer unless you add a forth parameter "di" in the > specification list such as > Sum[f, {i, imin, imax, di}] > > Can anyone help me to generate this second list? > > Thanks, Rob >