[Rcpp-devel] A strange question while using Rcpp

[晔张]

Hello, everyone.
I guess the probrem maybe occur because of sourceCpp(), so I have made
another test. I make a simple package using
RcppArmadillo.package.skeletion().
But the same problem appear.
My code is on Github:
https://github.com/ZhangYet/RcppTest
Is there anything related to my compiler or OS? I use 64-bit CentOS and g++
4.4.5


On Sat, Jan 18, 2014 at 2:01 AM, 张晔 <zhangyet at gmail.com> wrote:

> Thanks, Dirk.
> I have upload my code to Github: https://github.com/ZhangYet/RcppTest/
> And I made a mistake:
>
>
> | res1 <- mydcov(x,y)/sqrt(mydcov(x,x)*mydcov(y,y))
> |
> | a <- mydcov(x,y)
> | b <- mydcov(x,x)
> | c <- mydcov(y,y)
> | res2 <- a/sqrt(b*c)
> |
> | and res2 is different from res1.(res2 is the right answer.)
>
> I checked my test result. res2 is not the right answer, but it's different
> from res.
>
> 于 2014/1/17 21:36, Dirk Eddelbuettel 写道:
>
>  On 17 January 2014 at 20:51, 晔张 wrote:
>> | Dear all,
>> |
>> | I have a strange question such that I can't conclude it in the title.
>> | I have write an function:
>> | //[[Rcpp::export]]
>> | double mydcov(NumericVector x, NumericVector y)
>>
>> It would help us to see the function to have any guess at what may be
>> wrong.
>>   | This function is computing  ditance covariance. This function is OK.
>> It give
>> | the right answer.
>> | I use this function to compute distance correltion.
>> |
>> | //[[Rcpp::export]]
>> | double mydcor(NumericVector x, NumericVector y)
>> | {
>> |     return mydcov(x,y)/sqrt(mydcov(x,x)*mydcov(y,y));
>> | }
>> |
>> | Then, I compile the source code using sourceCpp.
>> | And then mydcor(x,y) give a wrong answer.
>> |
>> | Here comes the strange part:
>> | In R, I run code as follow
>> |
>> | res1 <- mydcov(x,y)/sqrt(mydcov(x,x)*mydcov(y,y))
>> |
>> | a <- mydcov(x,y)
>> | b <- mydcov(x,x)
>> | c <- mydcov(y,y)
>> | res2 <- a/sqrt(b*c)
>> |
>> | and res2 is different from res1.(res2 is the right answer.)
>> |
>> | And I have another test, rewriting the source code for mydcor():
>> | version1:
>> | //[[Rcpp::export]]
>> | double mydcor(NumericVector x, NumericVector y)
>> | {
>> |     double a = mydcov(x,y)
>> |     double b = mydcov(x,x);
>> |     double c = mydcov(y,y);
>> |     return (a/sqrt(b*c));
>> | }
>> |
>> | version2:
>> | //[[Rcpp::export]]
>> | double mydcor(NumericVector x, NumericVector y)
>> | {
>> |     double a = mydcov(x,y)
>> |     Rcout<<a<<"\n";
>> |     double b = mydcov(x,x);
>> |     Rcout<<b<<"\n";
>> |     double c = mydcov(y,y);
>> |     Rcout<<c<<"\n"
>> |     return (a/sqrt(b*c));
>> | }
>> | This time, version2 make a right answer.
>> | It's too weird. I havn't meet such situation before.
>>
>> I am not sure we are in a position to help you here.
>>
>> Regards, Dirk
>>
>> |
>> | Happy Lunar New Year (the most important festival in China), and Thanks
>> in
>> | advance.
>> |
>> | Best regards
>> | ZhangYet
>> |
>> | ----------------------------------------------------------------------
>> | _______________________________________________
>> | Rcpp-devel mailing list
>> | Rcpp-devel at lists.r-forge.r-project.org
>> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>
>
>
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