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Sum problem
*To*: mathgroup at smc.vnet.net
*Subject*: [mg65285] Sum problem
*From*: Majka Arkadiusz <Arkadiusz.Majka at telekomunikacja.pl>
*Date*: Fri, 24 Mar 2006 00:59:42 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
Hi ,
I have a problem that drives me crazy. In order to sum a (long) list of
elements (random numbers), say tab
tab = Table[Random[], {10^7}];
we use
In[3]:=
Plus@@tab
Out[3]=
4.999014220610286`*^6
....but to check Sum we get
In[6]:=
Sum[tab[[i]],{i,1,Length[tab]}]
Part specification K$30 is neither an
integer nor a list of integers.
There is no problem for
Sum[tab[[i]], {i, 1, 10^6}]
...and for
Sum[tab[[i]], {i, 1, 5*10^6}]
So Sum is ok. for number of elements of tab less than certain number that is
< Length[tab]
I also tested recursion methods (doSum[k_]:=doSum[k]=doSum[k-1] ...... Etc)
and got the same : fine but not for many elements (of course I set
$RecursiveLimit and $IterationLimit as Infinity)
I understand that to sum a list of elements we use Plus, Total etc but
nevertheless I want understand what I explained above.
Best,
Arek
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