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Re: Terrible unit trouble in Mathematic 9

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  • Subject: [mg129238] Re: Terrible unit trouble in Mathematic 9
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 23 Dec 2012 13:16:45 -0500 (EST)
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  • References: <kap6c4$469$1@smc.vnet.net> <kas2v5$ci1$1@smc.vnet.net> <20121221103924.B445A68CF@smc.vnet.net> <20121222100142.2CDC7687A@smc.vnet.net>

Thanks to Bob Hanlon, in a different post, using WolframAlpha to 
discover that one wants to use "AngularDegrees". That makes sense -- to 
disambiguate from "degrees" measuring temperature, I suppose.

Similar discovery reveals that you can get mils as a unit too, namely: 
"AngularMilsNIST". And that, evidently, to distinguish it from the unit 
of length (one thousandth of an inch).

There are so many units! No wonder Wolfram decided on the new model for 
units, using Quantity. Not as simple as all the old built-in symbols, 
since now we have text strings to name the units, but that seems the 
price to pay for so greatly extending the range of units allowed.


On Dec 22, 2012, at 5:01 AM, Murray Eisenberg <murray at math.umass.edu> wrote:

> This definitely seems to be an oversight (i.e., minor bug). What does work is:
>
>  UnitConvert[Quantity[0.81, "Radians"], Quantity[1, "Degrees"]]
>
> And, curiously, the following works:
>
>  UnitConvert[Quantity[0.81, "Radians"], "Grads"]
>
> (but the corresponding expression with "Mils" instead of "Grads" does not).
>
> On Dec 21, 2012, at 5:39 AM, jsheinwald <jsheinwald at comcast.net> wrote:
>
>> One problem with the UnitConvert command in Mathematica 9 is that it is not consistent.
>>
>>
>>
>> In[7]:= a = UnitConvert[Quantity[55, "Miles"/"Hours"], Quantity["Meters"/"Seconds"]]
>>
>> Out[7]= Quantity[96800/3937, ("Meters")/("Seconds")]
>>
>> Works.  But so does:
>>
>>
>> In[8]:= b = UnitConvert[Quantity[78, "Centimeters"/"Seconds"], "Inches"/"Minutes"]
>>
>> Out[8]= Quantity[234000/127, ("Inches")/("Minutes")]
>>
>> This, as expected works:
>>
>>
>> In[9]:= c = UnitConvert[Quantity[0.6, "Radians"], Quantity["Degrees"]]
>>
>> Out[9]= Quantity[34.3775, "AngularDegrees"]
>>
>> But this does not:
>>
>>
>> In[10]:= d = UnitConvert[Quantity[0.81, "Radians"], "Degrees"]
>>
>> During evaluation of In[10]:= UnitConvert::unkunit: Unable to interpret unit specification Degrees. >>
>>
>> Out[10]= UnitConvert[Quantity[0.81, "Radians"], "Degrees"]
>>
>> There are some serious consistency problems with the way unit conversions are implemented in Mathematica 9.  The examples in the help files could use some improvement too.
>>
>>
>>
>>
>>
>>
>> On Wednesday, December 19, 2012 4:55:49 AM UTC-5, David Reiss wrote:
>>> You need to get both the syntax right as well as the names of the
>>>
>>> units (which are strings).  E.g.,
>>>
>>>
>>>
>>> UnitConvert[Quantity[55 , "Miles"/"Hours"],
>>>
>>> Quantity["Meters"/"Seconds"]]
>>>
>>>
>>>
>>> Go back and spend a bit of time reviewing the documentation and
>>>
>>> working through the examples for the functions that are contained in
>>>
>>> the documentation....  ;-)
>>>
>>>
>>>
>>> --David
>>>
>>>
>>>
>>>
>>>
>>> On Dec 18, 2:35 am, tio54... at gmail.com wrote:
>>>
>>>> I continue to receive "Unable to interpret unit specification m/s" (for example, but almost anything I attempt returns this message) with input:
>>>
>>>> UnitConvert[55 mi/h,"m/s"] or UnitConvert[55 mi/h,m/s] or any other combination of quotes, omitted quotes, etc. Even the prediction/suggestion box,
>>> when I execute Quantity[55,"mi/hour"}, after it returns 55 mi/h, if I type in any combination of m/s, "m"/"s", "m/s", etc. into the box that opens when I select "Convert" in the prediction box yields the same "unable to interpret unit specification.
>>>
>>>>
>>>
>>>> What the heck????
>>
>
> ---
> Murray Eisenberg                                    murray at math.umass.edu
> Mathematics & Statistics Dept.     
> Lederle Graduate Research Tower            phone 413 549-1020 (H)
> University of Massachusetts                               413 545-2838 (W)
> 710 North Pleasant Street                         fax   413 545-1801
> Amherst, MA 01003-9305
>
>
>
>
>

---
Murray Eisenberg                                    murray at math.umass.edu
Mathematics & Statistics Dept.      
Lederle Graduate Research Tower            phone 413 549-1020 (H)
University of Massachusetts                               413 545-2838 (W)
710 North Pleasant Street                         fax   413 545-1801
Amherst, MA 01003-9305








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