[plt-scheme] Numerical precision (sqrt 2)

rw wrote:
> I am seeking a (hopefully built-in) way to decide the precision of
> irrational numbers. By default (PLT 4.1.5) gives:
>
> (sqrt 2) -> 1.4142135623730951
>
> I want to get an answer in (say) 50 or 100 digits precision. I am
> considering building a generating function for each digit of the
> irrational number, but I expect this to be computationally slow.
> Ideally, it would operate like this:
>
> (precision-take (sqrt 2) 50) -> 2^0.5 with 50 significant digits
>
> Is functionality like this already out there?
>
>   

(define (precision-sqrt n d)
  (/ (integer-sqrt (* n (expt 10 (* 2 d))))
     (expt 10 d)))

(precision-sqrt 2 50)

I would also suggest you to read 
http://docs.plt-scheme.org/guide/numbers.html for more understanding 
about PLT's number system.

Chongkai