r - Problems with sum functions -


using other programming language accelerate r big innovation, seems hazardous well. statistic function had stable use, given same result same entry such sum, sd, cor... problem have using big amount of data (10^8 sample). used rcpp , rcppparallel version of sum demonstrate bugs big data.

#include <rcpp.h> using namespace rcpp; /********************************************************  *           rcpp inner function :sum  *******************************************************/ // [[rcpp::export]] double rcppsum(numericvector x) {   return sum(x); }  /*** r   library("rcpp") library("rcppparallel")   options(digits=22)# showing more details in number     sourcecpp(system.file("tests/cpp/sum.cpp", package = "rcppparallel")) ##  given 2 function parallelvectorsum  (rcppparallel) , vectorsum (c++stl) ##  manipulated big vector   x<-rnorm(100000000)   (rsum<-sum(x))   (rcpp<-rcppsum(x))   (rcppparallel<-parallelvectorsum(x))   (std<-vectorsum(x))   identical(rsum,rcpp)   identical(std,rcpp)   identical(rsum,rcppparallel)   identical(rcpp,rcppparallel) ## simple checking of stability   v<-0 for(i in 1:100)v[i]<-sum(x)   (mean(v))   (sd(v)) ####stable sd =0   for(i in 1:100)v[i]<-vectorsum(x)     (mean(v))     (sd(v)) ###stable sd =0   for(i in 1:100)v[i]<-rcppsum(x)   (mean(v))   (sd(v)) ###stable sd =0    for(i in 1:100)v[i]<-parallelvectorsum(x)   (mean(v))   (sd(v)) ##instable sd!=0       */

we can qualify parallel version unstable, excluded. result between rcpp , rsum truth?

briefly:

  1. conjecture alert: seems hazardous well. please or remove it.
  2. please show courtesy of proper capitalization. write rcpp , rcppparallel, respectively. though guess refer labels doesn't matter.
  3. using options(digits=22) cute useless. double precision gives around 16 digits. hoping more not give more.

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