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Re: Quantity

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131726] Re: Quantity
  • From: Itai Seggev <itais at wolfram.com>
  • Date: Tue, 24 Sep 2013 04:16:35 -0400 (EDT)
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On Sun, Sep 22, 2013 at 02:47:41AM -0400, Bill Rowe wrote:
> On 9/21/13 at 4:35 AM, kessler.hannes at gmail.com (H. Ke=C3=9Fler) wrote:
> 
> >But what I am especially looking for is the list of the unit strings
> >in the correct spelling for Mathematica in
> >Quantity[magnitude,unitstring], not only the general overview of
> >units in the NIST-website. In the old Units-package (Mathematica 8
> >and earlier) each unit was a symbol and a list of all units
> >available could be obtained in the correct format and spelling by
> >?Units`*. This is obviously not possible anymore as there is no
> >package and all units are strings.
> 
> There does not seem to be a specific set of unit strings. Note
> that doing:
> 
> In[1]:= UnitConvert[Quantity[12., "Feet"], "Meters"]
> 
> Out[1]= 3.6576 m
> 
> returns a result essentially immediately. But doing
> 
> In[2]:= UnitConvert[Quantity[12., "Foot"], "Meters"]
> 
> Out[2]= 3.6576 m
> 
> returns the same result after a small delay. You should see a
> brief message indicating Mathematica is interpreting the units.
> I believe what is happening here is Mathematica is using Wolfram
> Alpha to interpret the unit string which increases the allowable
> number of unit strings significantly and makes it essentially
> impossible for a user to create a list of allowable unit strings.

I'm not sure if you are complaining about or praising the flexibility of input,
but you can always see the canonical unit name by looking at the InputForm.

In[3]:= Quantity[5, "Foot"]//InputForm
Out[3]//InputForm=
Quantity[5, "Feet"]

You can also turn off internet connectivity in the preferences if you don't
want Quantity to try to interpret units for you by asking W|A. 
--
Itai Seggev
Mathematica Algorithms R&D
217-398-0700 



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