Re: round off problem
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
<title></title>
</head>
<body bgcolor="#ffffff" text="#000000">
Mike, If EU stores atoms with double precision (i.e 15 places per the
manual) then any round off would be negligible over a fairly large
number of additions. The only problem comes on comparisons which I
would have to do something like this<br>
<br>
If abs(number1 - number2) > .001 <br>
<br>
for an equality test. If the difference is less than a penny then the
figures are equal , at least financially.<br>
<br>
george<br>
<br>
<br>
Mike Nelson wrote:<br>
<blockquote cite="mid928259027-1463792382-1088438917 at boing.topica.com"
type="cite">
</pre>
<blockquote type="cite">
<pre wrap="">I have imported general ledger data from a working system in
another OS
into mysql using Matt's ODBC tools. Trying to finish the EU general
ledger software, I've run into serious round off issues. Here's a
couple of examples to show the problem.
A typical account balance:
Mysql shows -1143.46 which is correct
EU trace shows -1143.459961 which is not accurate to 15 places as the EU
manual states.
Totalling the credits and debits over the entire file of transactions
gives the following (printing with a mask of %12.2f.)
Debits = 4642782.63
Credits= 4642782.56
Off by 4 cents. The input data from the other OS is balanced. It looks
like there's about 8 places of accuracy not 15.
The data records are always read into a sequence, then arithmetic is
done with atoms.
</pre>
</blockquote>
<pre wrap=""><!---->
Euphoria atoms are IEEE double precision floating points. They should never
be used for fiannical calculations, as many common decimal values cannot be
accuratrly represented in this type of value. For example, .01 has no finite
binary rerpesentation and therefor can't be exactly represented in an atom.
No doubt your source uses Binary Coded Decimal internally, which can
represent .01 exactly. (By the way BCD calculations are horribly slow vs
binary floating point and for this reason are never used except in finacial
calcualtions.)
Euphoria can't handle BCD directly but there are workarounds. If your totals
are constitently under 10,000,000 you can express all values in cents and
store them as Eu integers. If you are dealing with larger values, you will
need a libray for big numbers--check the contributions page.
-- Mike Nelson
</pre>
</blockquote>
</body>
</html>
|
Not Categorized, Please Help
|
|
