On 4 January 2011 at 15:14, Cedric Ginestet wrote:
| Happy new year to everyone,
|
| I have made a very straightforward comparison of the performance of standard
R,
| Rcpp function and sugar, and found that the latter produces the poorest
| performance. Let me know what you think and how I could improve such
| performance assessment.
|
| ###################################################
| Summing1 <- cxxfunction(signature(x="numeric"), '
| NumericVector xV(x);
| double out = sum(xV);
| return wrap(out);
| ',plugin="Rcpp")
| Summing2 <- cxxfunction(signature(x="numeric"), '
| NumericVector xV(x);
| double out = 0.0;
| for(int i=0; i<xV.size(); i++) out += xV[i];
| return wrap(out);
| ',plugin="Rcpp")
| ###################################################
| # Results.
| n <- 1000000; x <- rnorm(n)
| Summing1(x); Summing2(x); sum(x)
| #######################
| gives:
| [1] -396.6129
| [1] -396.6129
| [1] -396.6129
|
| ###################################################
| # Time.
| system.time(Summing1(x)); # Sugar
| system.time(Summing2(x)); # Rcpp
| system.time(sum(x)); # R-base
| ###################
| > system.time(Summing1(x));
| user system elapsed
| 0.016 0.000 0.016
| > system.time(Summing2(x));
| user system elapsed
| 0.008 0.000 0.011
| > system.time(sum(x));
| user system elapsed
| 0.000 0.000 0.003
|
|
| Sugar appears to be the slowest! What about Rcpp basic loop? Why isn't as fast
| as the standard sum() in R-base?
1) Try to think a about measurement error here; these times are all minuscule.
2) Consider reading the list archive, we have better use of benchmarks using
rbenchmark and replications; these are also some example in the examples
right in Rcpp
3) Consider reading the list archive and discussions about the NoNA tests.
4) Lastly, consider Romain's point about a baseline using an empty function.
Dirk
| Cheers,
| Cedric
|
| --
| 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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--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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