Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2012

[Date Index] [Thread Index] [Author Index]

Search the Archive

Puzzled by Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124570] Puzzled by Sum
  • From: Themis Matsoukas <tmatsoukas at me.com>
  • Date: Wed, 25 Jan 2012 07:03:32 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

I am trying to define a function F[X] whose argument is the upper limit in a summation:

A[i_, j_] := i/j + j/i
F[X_] := (Sum[A[i - j, j], {j, 1, i - 1}]) /. i -> X

but when I evaluate, say F[2], I get

-2 DifferenceRoot[{\[FormalY],\[FormalN]}\[Function]{(\[FormalN]-2) \[FormalY](\[FormalN])+(3-2 \[FormalN]) \[FormalY](\[FormalN]+1)+(\[FormalN]-1) \[FormalY](\[FormalN]+2)==0,\[FormalY](0)==0,\[FormalY](1)==-(1/2)}][2]-1

where the result should have been 2:

ii = 2;
Sum[A[ii - j, j], {j, 1, ii - 1}]

2

If I use A[i,j]=i j or other simple functions, everything works as expected.

Themis



  • Prev by Date: Re: compile a numerical integral
  • Next by Date: Re: Infinite Series Error - Bug?
  • Previous by thread: Re: UnitStep plotting
  • Next by thread: Re: Puzzled by Sum