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From |
Stas Kolenikov <skolenik@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: precision problem using double |

Date |
Sun, 16 Oct 2011 14:29:09 -0500 |

On top of NJC's response (which is on the spot, of course, as always), another useful function is -reldif- along with -epsfloat-/-espdouble- (which gives the relative accuracy, unlike the -smallestdouble- that gives a number that is way too small to be relevant): sysuse auto sum gear_ratio list if gear_ratio == 3.89 list if reldif(gear_ratio, 3.89) < 10*c(epsfloat) This comes handy in comparisons with fixed known constants. Of course, in your case, you should use -r(max)- which is a scalar with double precision (2e-16) rather than -`r(max)'- which is a string; if the latter is in scientific notation, it may have accuracy lower than 1e-15. On Sat, Oct 15, 2011 at 1:37 AM, Leandro Brufman <leandrobrufman@gmail.com> wrote: > Been reading some stuff on the precision of double, and how Stata > reads numbers for calculation (in particular this article > http://www.stata-journal.com/sjpdf.html?articlenum=dm0022) > But couldn't find a solution. Here's my problem: > > sum spread > br if spread==`r(max)' > > * it returns that there are no observations. > > sum spread > br if spread-`r(max)'<smallestdouble() > > *it also returns that there are no observations > > sum spread > gen test=spread-`r(max)' > > * the minimum number of variable test is -2.84217094e-14 > > any ideas on how to fix this code? i don't need a lot of precision, > but I do need to have these two lines working fine: > sum spread > br if spread==`r(max)' > > > as usual, many many thanks in advance... > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > -- Stas Kolenikov, also found at http://stas.kolenikov.name Small print: I use this email account for mailing lists only. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: precision problem using double***From:*Leandro Brufman <leandrobrufman@gmail.com>

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