Re: Formatting Decimals

On Mon, Jan 11, 2010 at 04:56:03PM -0500, tedd wrote: > > --Rick: > > The above described rounding algorithm introduces more bias than > simply using PHP's round() function, which always rounds down. IMO, > modifying rounding is not worth the effort. > > The "best" rounding algorithm is to look at the last digit and do this: > > 0 -- no rounding needed. > 1-4 round down. > 6-9 round up. > > In the case of 5, then look to the number that precedes it -- if it > is even, then round up and if it is odd, then round down -- or vise > versa, it doesn't make any difference as long as you are consistent. > > Here are some examples: > > 122.4 <-- round down (122) > 122.6 <-- round up (123) > 122.5 <-- round up (123) > > 123.4 <-- round down (123) > 123.6 <-- round up (124) > 123.5 <-- round down (123) > > There are people who claim that there's no difference, or are at odds > with this method, but they simply have not investigated the problem > sufficiently to see the bias that rounding up/down causes. However, > that difference is very insignificant and can only be seen after tens > of thousands iterations. PHP's rounding function is quite sufficient. This is called (among other things) "banker's rounding". But PHP's round() function won't do banker's rounding, as far as I know. Paul -- Paul M. Foster