From wsi@gcal.ac.uk  Thu Sep 13 09:43:08 2001
From: wsi@gcal.ac.uk (wsi@gcal.ac.uk)
Date: Thu, 13 Sep 2001 10:43:08 +0200 (MET DST)
Subject: [Rd] sum overflow (PR#1091)
Message-ID: <200109130843.KAA28348@pubhealth.ku.dk>

Full_Name: Bill Simpson
Version: 1.2.3
OS: linux
Submission from: (NULL) (193.62.250.209)


I think I have found an accuracy problem with sum()

> a<-1:1000
> b<-1:1000
>
> crossprod(a,a)*crossprod(b,b)
             [,1]
[1,] 1.114448e+17
> drop(.Last.value)
[1] 1.114448e+17
>
#this should give same answer as above
> sum(a*a)*sum(b*b)
[1] -652010736
#seems to be due to sum using integer representation which overflows instead of
using
#double representation

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[Rd] sum overflow (PR#1091)
wsi@gcal.ac.uk