With very kind & generous help of Robert Samal following solution was proposed:
bool(x.n() != NaN) should give out True iff x is a real number. It seems to work: http://aleph.sagemath.org/?z=eJxLVLBV0DXUNzTSKshU0FYAs4oLi0o0DM0gIgWZcUZAysjUTBNImegbcyUBtSQWJSfnF2sYaXJxFRRl5pUoJOXn52gk6uVpaCoo2ir4JfppIkskIUsAAIR8Hfg%3D Is this a correct & proper method to recognize real numbers? On Saturday, April 28, 2012 6:40:55 PM UTC+2, Volker Braun wrote: > > The floating point "fields" in Sage (RR or RDF) can represent both > infinity and NaN. So you'll have to check separately if this is the case. > Note that "x in RR" checks that x can be represented in RR. > > > > On Saturday, April 28, 2012 7:38:44 AM UTC-4, Duc Trung Ha wrote: >> >> Hola, >> >> I'm stuck at the problem of determinating whether a given expression is >> known to be real number or not. >> >> >> >> >> So far, I've been testing this either >> with >> >> >> expr.is_real() >> >> >> >> or >> >> >> >> expr in >> RR >> >> >> >> succesfully. >> >> Now, if I give Sage this expression of real number: >> -1/12*pi + 1/12*sqrt(16*pi + pi^2 + 256) + 4/3 >> the following results will occur: >> >> http://aleph.sagemath.org/?z=eJxLVLBV0DXUNzTSKshU0FYAs4oLi0o0DM0gIgWZcUZAysjUTBNImegbc3EVFGXmlSgk6mUWxxelJuZoaMKFFDLzFIKCAHCUFik%3D >> >> On the other hand, non-real value below: >> arccos(2) >> would produce the very same results, though it should give opposite >> results for at least 1 test: >> >> http://aleph.sagemath.org/?c=a+%3D+arccos%282%29%0A%0Aprint+a.is_real%28%29%0A%0Aprint+a+in+RR >> >> Is there any other/standard way to test membership to real numbers? >> >> Is this a bug or is it covered somewhere else? >> Duc Trung Ha >> Sage Version 4.8, Release Date: 2012-01-20 >> Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz >> Kubuntu 12.04 >> > -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
