[R] Determinant

[Boris Steipe]

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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