[S] Summary: RE: Problems in generating Random Numbers

Smith, Stephen (SmithSJ@mar.dfo-mpo.gc.ca)
Mon, 01 Jun 1998 10:53:46 -0300

On the 25th of May I had reported a problem with using sample() to
conduct a simulation and having .Random.seed reset back to the same
number. Earlier Patrik OHagen had reported a similar problem with
cov.mve which was confirmed by Brian Ripley.

Thanks to Stephen Weller from Mathsoft for his quick assistance.

It appears that Patrik's and my problems had a similar basis:

cov.mve resets .Random.seed internally and therefore any simulation with
this function will run into problems. A fix to this problem requres
change to the code with an option to change the seed. The specific code

class(ans) <- "mve"
attr(ans, "call") <- sys.call()
if(!missing(mutate.prob)) {
if(length(mutate.prob) != 4)
stop("mutate.prob must have length 4")
if(any(mutate.prob < 0))
stop("negative value in mutate.prob")
if(sum(mutate.prob[2:4]) > 1)
stop("sum of last 3 mutation probabilities
greater than 1")

In may case, I use jackknife() later on my code which defaults to seed=0
in its call statement:

> args(jackknife)
function(data, statistic, args.stat = NULL, seed = 0, group.size = 1,
assign.frame1 = F)

This feature can be by-passed by conducting the simulation with
something like seed=sample(1000,1) in the call statement.

Stephen Smith

Stephen J. Smith
Head, Molluscan Fisheries Section
Invertebrate Fisheries Division
Department of Fisheries and Oceans
P.O. Box 1006
Dartmouth, Nova Scotia
Canada B2Y 4A2

Street address for Couriers:
1 Challenger Drive

Voice: 902-426-3317
Fax: 902-426-1862
Note new email address.
Internet: Smithsj@mar.dfo-mpo.gc.ca

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