[R] Determinant
Boris Steipe
boris.steipe at utoronto.ca
Thu May 14 21:17:23 CEST 2015
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 (http://www.burns-stat.com/documents/tutorials/impatient-r/more-r-key-objects/more-r-numbers/) 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.
Cheers,
B.
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 determinant.
>
> 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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