[Date Index] [Thread Index] [Author Index]
Re: Re: "Assuming"
Mariano SuÃ¡rez-Alvarez wrote: > On Feb 23, 7:34 am, Daniel Lichtblau <d... at wolfram.com> wrote: > [...] >>[From David Cantrell:] >> >>>>[...] But I do know of a case where >>>>Mathematica goes even further, removing a singularity at which the >>>>function >>>>is defined as a number: >> >>>>In:= FullSimplify[UnitStep[-x^2]] >>>>Out= 0 >> >>>>despite the fact that correctly >> >>>>In:= UnitStep[-x^2] /. x -> 0 >>>>Out= 1 >> >>>>Perhaps the simplification above is considered a bug, perhaps not. >> >>>>David >> >>A feature, really. That is, it's wrong, but FullSimplify can make >>mistakes on measure zero sets. We do not generally regard this >>phenomenon as a bug, though we reconsider on case by case basis. > > > How does that `measure zero' allowance work in a context > of something like > > Assuming[Element[x, Integers], FullSimplify[something]] > > ? > > -- m I've seen cases where the FullSimplify[something] result differs from something on a finite set of integers. This motivated me several months ago to alter assumptions of integrality, to reality (realness? realhood?), in processing of Integrate. Daniel Lichtblau Wolfram Research