MathGroup Archive 2012

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

Search the Archive

unexpected behaviour of Sum

I do not want to say that this is a bug, however I did
not find, in the Sum documentation, an explanation of this
behaviour (v8.0.4)

I defined an innocent function like
that compute the sum of the digits of a number.
(I tried with other functions, so the culprit is not IntegerDigits)

Then I compute two sums:
Sum[sod[k],{k,10^6}] which gives 27000001 (ok)
Sum[sod[k],{k,1+10^6}] which gives 500001500001 (nonsense).
Sum[sod[k],{k,2,1+10^6}] which gives 27000002 (ok)

so, it seems to me that Sum has a problem when the iterator
works in a range greater than 10^6.

Indeed, I made an experiment:
I set L={}; and defined
Then Sum[sod[k],{k,1+10^6}] still gives 500001500001 
and at the end L is equal to {k}, so it seems that
Sum tried to do something symbolic (??).

Is this a bug or a feature whose documentation I was not
able to find? Say, is there an option to fix things ?

Btw, using ParallelSum instead of Sum works fine (and faster).

  • Prev by Date: Re: Speed of Mathematica on AMD machines
  • Next by Date: Re: does siri use mathematica?
  • Previous by thread: Re: Is Mathematica v8 slower than v7 ?
  • Next by thread: Re: unexpected behaviour of Sum