Re: Integrate UnitStep, Bug?

*To*: mathgroup at smc.vnet.net*Subject*: [mg50344] Re: Integrate UnitStep, Bug?*From*: DrBob <drbob at bigfoot.com>*Date*: Sat, 28 Aug 2004 04:37:56 -0400 (EDT)*References*: <20040827101518.072$C0@newsreader.com> <opsdedkcwuiz9bcq@monster.cox-internet.com> <001601c48c4e$e1e75b30$b5803e44@Dell>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

Those are the plots I'm seeing, and I stand corrected. I obviously had some kind of brain fart! Bobby On Fri, 27 Aug 2004 16:59:48 +0100, David W. Cantrell <DWCantrell at sigmaxi.org> wrote: >> We're evidently not seeing the same plots. > > I'm running version 5.0.0 under Windows XP. > For the first plot you mentioned, my Mathematica shows the function to be > 1 between e=0 and e=2, and 0 elsewhere. > For the second plot you mentioned, my Mathematica shows the function to be > 1 between e=0 and e=3, and 0 elsewhere. > Are those not the plots you're getting? > Anyway, the plots on my machine are correct (well, except for the spurious > vertical line segments, which I'm sure you've learned to ignore in such > cases). Those plots are of course consistent with the answer Min[a,b], > which I had verified by hand long before I saw your original post. > > Regards, > David Cantrell > >> On Fri, 27 Aug 2004 10:15:18 -0400 (EDT), David W. Cantrell > <DWCantrell at sigmaxi.org> wrote: >> >> > DrBob <drbob at bigfoot.com> wrote: >> >> I think both results are wrong, and the correct answer is Abs[b-a]. >> > >> > I have no idea why you think that's the correct answer, especially > since >> > the plots which you mention below are correct (at least on my machine) > and >> > clearly show that Abs[b-a] is incorrect. >> > >> > A correct answer was already given by jens: Min[a,b]. >> > >> >> Unless these Plots are wrong? >> >> >> >> fr[e_] := UnitStep[-e]; >> >> fl[e_] := UnitStep[-(e - b)]; >> >> >> >> b = 2; a = 3; >> >> Plot[fl[e](fr[e - a] - fr[e]), {e, -5, 5}, PlotStyle -> >> >> {Thickness[0.01]}] >> >> >> >> b = 5; a = 3; >> >> Plot[fl[e](fr[e - a] - fr[e]), {e, -5, 5}, PlotStyle -> >> >> {Thickness[0.01]}] >> >> >> >> Bobby >> >> >> >> On Thu, 26 Aug 2004 06:50:47 -0400 (EDT), <jens at fika.de> wrote: >> >> >> >> > The following code returns the incorrect result (-a+b) > UnitStep[a-b]. >> >> > It should be Min[a,b]. >> >> > >> >> > fr[e_]=UnitStep[-e]; >> >> > fl[e_]=UnitStep[-(e-b)]; >> >> > Integrate[fl[e](fr[e-a]-fr[e]),{e,-Infinity,Infinity}, >> >> > Assumptions->{b>0,a>0}] >> >> > >> >> > Is this a known bug? Should I avoid using step functions with >> >> > Integrate? >> > >> > This is clearly a bug. Whether it's previously known or not, I have no >> > idea. It needs to be fixed! It would be hard to "avoid using step > functions >> > with Integrate" in many cases. >> > >> > David Cantrell >> > >> > >> >> >> >> -- >> DrBob at bigfoot.com >> www.eclecticdreams.net > > > -- DrBob at bigfoot.com www.eclecticdreams.net