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Re: Help please: Summing a list

  • To: mathgroup at
  • Subject: [mg13507] Re: [mg13480] Help please: Summing a list
  • From: "Jens-Peer Kuska" <kuska at>
  • Date: Fri, 31 Jul 1998 04:33:23 -0400
  • Sender: owner-wri-mathgroup at

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

a) Mathematica List[]s index starts with 1, Part[any,0] gives the head.
So Your summation
   must be

b) What do You want ? A function PP[i_] ? that calculates the sums ?
    Here is a possible solution


  or the recursive one

  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


Hope that helps

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