Hello everybody. I'm currently working on a simple raytracer. No the time has come to adjust my EPSILON value (eg. for comparing doubles). What is a good value for it? At the momant I have 1e-10 but I'm not long enought confirm with C to say that this value is optimal. Thank you for response.
It does depend a little bit on what you're trying to do and what range your numbers are, but if your numbers are relatively small (+/-1.0..100.0 or so) then your value will be fine.
--
Mats
Somewhere between 12 to 15 decimal places to the right of the smallest values you care about.
You need to look at the range and precision of the values you're storing to begin with.
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If you wanted to, you could calculate an epsilon at runtime. Using something like pow(10, log10(number)-15), assuming that your doubles have 15 digits, might work. Of course this would be quite slow, so unless you have wildly variable values, use a hard-coded value.
I think there may be a constant called DBL_DIGITS in <float.h> which tells you how many digits of precision a double has, but I'm not sure how portable it is.
dwk
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I think it is DBL_DIG, according to C99.I think there may be a constant called DBL_DIGITS in <float.h> which tells you how many digits of precision a double has, but I'm not sure how portable it is.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
Thank you for this good answers!
Yes, that's it. There's also DBL_DIGITS in some implementations, but it's less portable.
dwk
Seek and ye shall find. quaere et invenies.
"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell
Other boards: DaniWeb, TPS
Unofficial Wiki FAQ: cpwiki.sf.net
My website: http://dwks.theprogrammingsite.com/
Projects: codeform, xuni, atlantis, nort, etc.
