From: Ted Harding <Ted.Harding_at_nessie.mcc.ac.uk>

Date: Thu 09 Feb 2006 - 00:26:13 EST

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> This isn't really something that can be proved by a test. Perhaps the

*> current implementation makes those equal only because 500 is even, or
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*> divisible by 5, or whatever...
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*>
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*> I think the intention is that those should be equal, but in a quick
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*> search I've been unable to find a documented guarantee of that. So I
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*> would take a defensive stance and assume that there may be conditions
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*> where c(rnorm(m), rnorm(n)) is not equal to rnorm(m+n).
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*>
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*> If someone can point out the document I missed, I'd appreciate it.
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*>
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*> Duncan Murdoch
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E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> Fax-to-email: +44 (0)870 094 0861

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Feb 09 00:42:30 2006

Date: Thu 09 Feb 2006 - 00:26:13 EST

On 08-Feb-06 Duncan Murdoch wrote:

> On 2/8/2006 4:53 AM, Bjørn-Helge Mevik wrote:

>> Why don't you test it yourself? >> >> E.g., >> >> set.seed(42) >> bob1 <- rnorm(1000,0,1) >> set.seed(42) >> bob2 <- rnorm(500,0,1) >> bob3 <- rnorm(500,0,1) >> identical(bob1, c(bob2, bob3)) >> >> I won't tell you the answer. :-)

> This isn't really something that can be proved by a test. Perhaps the

On my understanding, once the seed is set the sequence generated by the underlying RNG is determined, whether it is the result of a single call to produce a long sequence or multiple calls to generate many shorter sequences. Example:

*> set.seed(42)
**> multi<-numeric(20)
**> set.seed(42)
**> single<-rnorm(20)
**> set.seed(42)
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> for(i in (1:20)) multi[i]<-rnorm(1)

> print(max(multi-single),digits=22)

[1] 0

> print(min(multi-single),digits=22)

[1] 0

In other words: identical!

Whether there are possible exceptions, in some implementations of r<dist> where <dist> is other than "norm", has to be answered by people who are familiar with the internals of these functions.

Best wishes to all,

Ted.

E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> Fax-to-email: +44 (0)870 094 0861

Date: 08-Feb-06 Time: 13:26:10 ------------------------------ XFMail ------------------------------ ______________________________________________R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Feb 09 00:42:30 2006

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