wdunlap at tibco.com
Fri May 15 00:12:41 CEST 2015
Note that when using double precision arithmetic you cannot tell
if that number is different from other numbers within 10 billion of
it -- they all have the same representation.
> 1.6777215999999849e+29 == 1.6777215999999849e+29 + 1e10
You need to use other, time consuming, methods (e.g., arbitrary
precision arithmetic such as in the Rmpfr package, or some
On Thu, May 14, 2015 at 12:17 PM, Boris Steipe <boris.steipe at utoronto.ca>
> Of course the number _is_ an integer. It seems you are asking whether that
> integer can be exactly _represented_ on a computer? That depends on your
> processor (eg. 32/64 bit) and the size of the number; alternatively you
> could calculate with arbitrary precision with the Rmpfr package.
> For more insights, have a look at Pat Burs' summary of number
> representation in R (
> and/or read chapter one of his R inferno.
> Or, maybe you can state more clearly what you are trying to achieve in the
> end, there might be other options.
> On May 14, 2015, at 4:44 AM, chasiotisv at math.auth.gr wrote:
> > Hello,
> > I am Vasilis Chasiotis and I am a candidate Ph.D. student in Aristotle
> University of Thessaloniki in Greece.
> > I have the following problem.
> > I want to check if the square of a number ( for example the square of
> 1.677722e+29 ) is an integer.
> > The problem is that this number is the calculation of the determinant
> (so the number should be an integer) of a matrix 22x22, which means it has
> an approximation ( the "real" number is 1.6777216e+29 but R gives to me
> 1.6777215999999849e+29 ), because R use LU-decomposition to calculate the
> > That means that the radical of the number 1.6777215999999849e+29 is not
> an integer, but it should be.
> > How can we overcome this problem?
> > Thank you in advance.
> > I look forward to hearing from you soon.
> > Vasilis Chasiotis
> > ______________________________________________
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> > PLEASE do read the posting guide
> > and provide commented, minimal, self-contained, reproducible code.
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> PLEASE do read the posting guide
> and provide commented, minimal, self-contained, reproducible code.
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