[Rcpp-devel] Summing over a numeric vector.

[Cedric Ginestet]

Thanks Douglas,
How stupid of me!
Cheers,

On 03/01/11 16:00, Douglas Bates wrote:
> You forgot to initialize i in both loops.  It should be
>
> for(int i = 0; i<  Ne; i++)
>
> On Mon, Jan 3, 2011 at 9:50 AM, Cedric Ginestet
> <c.ginestet05 at googlemail.com>  wrote:
>> Dear Rcpp experts,
>>
>> I have the following bizarre problem. Although the second summing C++
>> function seems easier than the former, it does not produce the correct
>> answer. See the following reproducible codes:
>>
>> ##########################################
>> Summing1<- cxxfunction(signature(x="numeric"), '
>>      Rcpp::NumericVector Dvec(x);
>>      int Ne = Dvec.size();
>>      double out =0;
>>      for(int i; i<Ne; i++) out += (1/Dvec[i])/Ne;
>>      return Rcpp::wrap(out);
>> ',plugin="Rcpp")
>> x<- rnorm(100)
>> Summing1(x); mean(1/x)
>> ##########################################
>> gives:
>> [1] 0.02950222
>> [1] 0.02950222
>>
>> ##########################################
>> Summing2<- cxxfunction(signature(x="numeric"), '
>>      Rcpp::NumericVector Dvec(x);
>>      int Ne = Dvec.size();
>>      double out =0;
>>      for(int i; i<Ne; i++) out += Dvec[i];
>>      return Rcpp::wrap(out);
>> ',plugin="Rcpp")
>> x<- rnorm(100)
>> Summing2(x); sum(x)
>> ############################################
>> gives:
>> [1] 0
>> [1] -9.220588
>>
>> Any help greatly appreciated.
>> Cheers,
>>
>>
>> --
>> Cedric Ginestet
>> Centre for Neuroimaging Sciences (L3.04)
>> NIHR Biomedical Research Centre
>> Institute of Psychiatry, Box P089
>> Kings College London
>> De Crespigny Park
>> London
>> SE5 8AF
>>
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>>