Re: Help please: Summing a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg13507] Re: [mg13480] Help please: Summing a list*From*: "Jens-Peer Kuska" <kuska at linmpi.mpg.de>*Date*: Fri, 31 Jul 1998 04:33:23 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Hi Rob, >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}]; a) Mathematica List[]s index starts with 1, Part[any,0] gives the head. So Your summation must be Sum[P[[n]],{n,1,i}] b) What do You want ? A function PP[i_] ? that calculates the sums ? Here is a possible solution PP[i_]:=PP[i]=Module[{n},Sum[P[[n]],{n,1,i}]] or the recursive one PP[1]:=P[[1]] PP[i_ /; i>1]:=PP[i]=P[[i]]+PP[i-1] Notice that this definition does not calculate the sums. But if You say PP[4] You will get the value. Or do You want that PP is a list containing the accumulated sums ? PPList = Table[Plus @@ Drop[#1,n] &[P],{n,-10,0}] or using the defined PP[]-Function PPList=Table[PP[i],{i,1,11}] Hope that helps Jens