[Rcpp-devel] A strange question while using Rcpp

[晔张]

Thank you, Romain!
There are several double variables which I didn't init in my code.
It's all right, now.


On Sun, Jan 19, 2014 at 9:42 PM, Romain Francois
<romain at r-enthusiasts.com>wrote:

> Hello,
>
> This stands out
>
> double U;
>   for(int i=0; i<n; i++){
> for(int j=0; j<n; j++){
> U = U + A_kl(i,j) * B_kl(i,j)/n/n ;
> }
>   }
>   U = sqrt(U);
>
> U is not initialized. so all bets are on. Anything can happen. Same holds
> for aa and bb.
>
>
> Also, in terms of how you use attributes, you can at your advantage
> replace things like this:
>
> //[[Rcpp::export]]
> double mydcov(SEXP X, SEXP Y) {
>    NumericVector x = as<NumericVector>(X);
>    NumericVector y = as<NumericVector>(Y);
>    …
> }
>
> by things like this:
>
> //[[Rcpp::export]]
> double mydcov(NumericVector x, NumericVector y){
>    …
> }
>
> Romain
>
> Le 19 janv. 2014 à 14:09, 晔张 <zhangyet at gmail.com> a écrit :
>
> 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
>>>
>>
>>
> _______________________________________________
> 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
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/rcpp-devel/attachments/20140119/12e4347b/attachment-0001.html>