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Why doesn't Quantity[] and related functions work for me?

I'm a new user of MMA ver. 10.3.0 Home Edition. I'm trying to learn how to use Units, but it's not working. For example

In[47]:= UnitConvert[Quantity[12, "Meters"/"Seconds"], "Miles"/"Hours"]

Out[47]= UnitConvert[
 QuantityUnits`Private`ToQuantity[
  QuantityUnits`Private`UnknownQuantity[12, ("Meters")/(
   "Seconds")]], ("Miles")/("Hours")]

If I load the Units` package I get the answer I seek:

In[48]:= << Units`

Convert[12  Meter/Second, Mile/Hour]

Out[49]= (37500 Mile)/(1397 Hour)

But starting with ver 9 I shouldn't have had to do that. Any ideas about what's going on?
POSTED BY: Victor Bloomfield
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POSTED BY: Gustavo Delfino
Dana DeLouis
Dana DeLouis
Posted 9 years ago
POSTED BY: Dana DeLouis
POSTED BY: Victor Bloomfield
Dana DeLouis
Dana DeLouis
Posted 9 years ago
POSTED BY: Dana DeLouis

It is probably worth clarifying that this is presumably a sporadic issue--I have never encountered it (Mac installation) and the various folks that I work with who are using a similar installation have not encountered it. As in all cases where something is not working that clearly should work, it's best to contact Wolfram technical support to get the inside track as Dana DeLouis did.

POSTED BY: David Reiss

"Any port in a storm." I'm glad it's working now!
POSTED BY: David Reiss

In fact, I just checked by trying to load Units, and got a "Cannot open "Units`" $Failed result. So whatever I did earlier seems to have provoked a proper upgrade of the installation.
POSTED BY: Victor Bloomfield
POSTED BY: Victor Bloomfield
POSTED BY: Victor Bloomfield

But note that, as I mention above, the Needs["Units`"] causes an outdated component to be used instead of the new updated and expanded version for interpreting units that is now contained within Mathematica's default codebase. So as I mentioned above, you should remove that from the init.m file. If then, upon restarting Mathematica, you still have the same problem, I would suggest that you contact Wolfram support for advice on resolving this issue.

POSTED BY: David Reiss

Actually I see now that you were getting as a result the Private context expression -- my mistake. ;-)

My comment about not using the Needs["Units`"] package still holds, but there is something wrong with your setup which a bona fide Wolfram employee may comment on. One thing to try is to execute 

RebuildPacletData[]

as well as restart Mathematica.

Sorry for the confusion!
POSTED BY: David Reiss

It is not clear why you are trying to use things in the 

QuantityUnits`Private`

context like

QuantityUnits`Private`ToQuantity

That is certainly not the correct way to proceed--almost always avoid using undocumented functions and always avoid using anything in a Private context. For your particular example the correct syntax is 

UnitConvert[Quantity[12, ("Meters")/("Seconds")], ("Miles")/("Hours")]

And I would suggest removing Needs["Units`"] from the initi.m file as it will load a legacy pacage that was superceeded by internal Mathematica functionality as of version 9. See

http://reference.wolfram.com/language/Compatibility/tutorial/Units.html
POSTED BY: David Reiss

That seems to have done the trick. Thanks.
POSTED BY: Victor Bloomfield

I don't know the reason why it does not work by default. The code you posted works fine for my Mathematica. However if you'd like to work it around, editing the init.m file in C:\ProgramData\Mathematica\Kernel should do the trick. Simply add 

Needs["Units`"]

at the end of the file.
POSTED BY: Wojciech Artichowicz
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