[pltscheme] Numerical precision
From: Jaime Vargas (jev at mac.com)
Date: Wed Mar 11 12:31:54 EDT 2009 

Hi,
I am doing some personal financial simulations and need math procedures
that keep N digits of numerical precision. For this I am using
Scheme's exact
numbers and wrote the attached naive implementation.
Given that I am no math guru is there something that I should worry
about
this implementation? Also, I would like to optimize the round:N
procedure to
avoid calculating N and 1/N all the time. I thought that LET will
help, but it did
not.
Thanks,
Jaime E Vargas
#lang scheme
(provide numericalprecision
(renameout [round:N round]
[*:N *]
[/:N /]
[+:N +]
[:N ]))
(define numericalprecision (makeparameter 2))
(define (N)
(expt 10 (numericalprecision)))
(define (1/N)
(/ 1 (N)))
(define (round:N x)
(* (1/N) (round (* x (N)))))
(define (*:N . nums)
(round:N (apply * nums)))
(define (/:N . nums)
(round:N (apply / nums)))
(define (+:N . nums)
(round:N (apply + nums)))
(define (:N . nums)
(round:N (apply  nums)))