On Mon, 22 Mar 2004, Rajarshi Guha wrote: > Hello, > I have some C code that I'm interfacing to R using the .C calling > interface. Currently the C code uses the rand() function from the GNU C > library to generate random numbers. Since I need the random numbers in a > range from 0 to a (where a is an integer) I use the RAND_MAX macro as > > (int)(rand() * (float)(*nobs-1) / (RAND_MAX+1.0)) > > (taken from the rand() manpage)
That isn't a random *number*: it is a random *integer*. It is a random integer on 0, ..., a=*nobs-2: is that what you wanted? > However, since I have access to the R RNG's I'd like to use them. > > Firstly, would it be an improvement to use the R RNG over that supplied > by the C library? Most likely. > Secondly, I dont see any mention of an equivilant to RAND_MAX in the > documentation of runif() (as I want to use unif_rand() in my C code). That's because runif() is documented to return a *double*, and unif_rand() a uniform(0,1) *double*. This is in `Writing R Extensions'. > Is it valid to use the C libraries' RAND_MAX as the maximum value of the > RNG or am I missing something? That the C rand() is *integer*. > As far as I understand using the .C interface I can't call R functions > from my C code (which means I cant access runif()) - is this correct? > As I would rather stay with the .C interface rather than the .Call > interface is there a way to get random numbers within a given range? a + (b-a) * unif_rand() for U(a, b) (int) (a * unif_rand()) for a random integer in 0, ... , a - 1. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
