On 1 September 2011 at 14:23, Zhongyi Yuan wrote: | If there is a seed set in R before rngs() is called, then "RNGScope z;" can be | omitted, right?
Don't think about it this way. Think about properly initializing the state of the RNG, and instantiating a local RNGScope variable does that. Which is why we strongly recommend that usage pattern. | I used to use RNGScope() to set seed. I guess that is not the right way, is it? | | My test shows, with RNGScope(), even if I re-compile (without quitting R), rngs | always gives the same numbers. I have to quit R and then re-compile to get | random numbers. There is no such problem with "RNGScope z". I don't quite understand what you are trying to say here. To get different numbers, you need different seeds. Initializing based on the clock (and/or process id) is a common trick to ensure this. Don't get me wrong but this now seems to have little to do with Rcpp; you may want to read up on random numbers, simulations and do some experiments with plain C or C++ code. Please do not abuse this list as a substitute for doing your independent study and reading. Dirk | Zhongyi | | On Thu, Sep 1, 2011 at 12:15 PM, Dirk Eddelbuettel <[email protected]> wrote: | | | I should have written that quick function as follows: | | rngs <- cxxfunction(signature(), plugin="Rcpp", | body="RNGScope z; return Rcpp::rnorm | (5,0,1);") | | You _do_ want RNGScope around; my bad for omitting it in the previous post. | | Dirk | | -- | Two new Rcpp master classes for R and C++ integration scheduled for | New York (Sep 24) and San Francisco (Oct 8), more details are at | http://dirk.eddelbuettel.com/blog/2011/08/04# | rcpp_classes_2011-09_and_2011-10 | http://www.revolutionanalytics.com/products/training/public/ | rcpp-master-class.php | | -- Two new Rcpp master classes for R and C++ integration scheduled for New York (Sep 24) and San Francisco (Oct 8), more details are at http://dirk.eddelbuettel.com/blog/2011/08/04#rcpp_classes_2011-09_and_2011-10 http://www.revolutionanalytics.com/products/training/public/rcpp-master-class.php _______________________________________________ Rcpp-devel mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
