
From:  George Barrick 
Subject:  Re: Is this a numerical problem? 
Date:  Thu, 19 Aug 2010 10:38:27 0400 
Re: Is this a numerical problem? 2010.08.19.14:16:35
UT Hey GNUOctave folks, May I suggest that you cut the guy some slack? Lukas, that is. You should not be telling him to submit a bug report, because the phenomenon that he is describing is not a bug. If you're telling him to submit because his bug report will be ignored; OK. A lot of the people who use Octave do not have a thorough and complete education about the issues that come up with the representation of rational numbers as binary floatingpoint. The thing is, that we're using 64 bits to describe a number, of which twelve are used as exponent. Just 56 bits make up the mantissa (some IEEE formats use tricks to achieve 57). The question a user should always ask is: Can my number be represented exactly using 56 bits? or Can the number be represented exactly in base 16 using 14 hexadecimal digits? If the answer is yes, then the floating point representation will not have much effect upon rounding, truncation, modulus calculations, etc. If the answer is no, then the user should expect the unexpected. I'm just saying that, on a forum such as this, we should give the guy a scientific answer. We should not be flippant, and tell him to submit a bug report that will be ignored. George gbarrick_at_kent_dot_edu gbarrick_at_walsh_dot_edu 
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