Re: Units question

*To*: mathgroup at smc.vnet.net*Subject*: [mg115571] Re: Units question*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Sat, 15 Jan 2011 04:44:07 -0500 (EST)

If units being positive doesn't make sense, why is the solution simply making them positive? Bobby On Fri, 14 Jan 2011 05:19:43 -0600, Bob Hanlon <hanlonr at cox.net> wrote: > > Dimensions aren't numbers, so being positive doesn't make sense. It is a > just convenient to say that they are positive to trick Sqrt and the > like. In some cases using this is better than using PowerExpand since > PowerExpand would affect the treatment of variables not just the > dimensions. You can handle all of the dimensions at once: > > Needs["Units`"] > > simplifyUnits = ToExpression[# <> " > 0" & /@ Names["Units`*"]]; > > Simplify[Sqrt[Meter^2/Second^2] Second/Meter^2, simplifyUnits] > > 1/Meter > > > Bob Hanlon > > ---- Murray Eisenberg <murray at math.umass.edu> wrote: > > ============= > Even after loading the Units package, Mathematica doesn't know that > Meter and Second are positive. > > My naive sense is that this is just plain stupid. Am I missing something > here? > > On 1/12/2011 4:07 AM, Bob Hanlon wrote: >> Simplify[Sqrt[Meter^2/Second^2] Second/Meter^2, >> {Meter> 0, Second> 0}] >> >> 1/Meter >> >> >> Sqrt[Meter^2/Second^2] Second/Meter^2 // PowerExpand >> >> 1/Meter >> >> >> Bob Hanlon >> >> ---- Ted Sariyski<tsariysk at craft-tech.com> wrote: >> >> ============= >> Hi, >> Working with units I get correct result: >> >> Sqrt[Meter^2/Second^2] Second)/Meter^2 >> >> How to tell Mathematica to simplify the result to Meter^-1? >> Simplify and FullSimplify doesn't do the job. >> Thanks in advance, >> --Ted >> >> > -- DrMajorBob at yahoo.com