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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?

14 Replies

That seems to have done the trick. Thanks.

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
POSTED BY: David Reiss

But note that, as I mention above, the Needs["Units`"] causes an outdated component to be used instead of the new updated and expanded version for interpreting units that is now contained within Mathematica's default codebase.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

For some reason, the old behavior of the Units package no longer persists after I did what I described. Convert[ ] no longer is recognized as a function, but UnitConvert[ ] now is. So I think that the automatic(?) upload from the Wolfram site, triggered by the restart after addition to the init.m file, updated the program properly.

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.

"Any port in a storm." I'm glad it's working now!

POSTED BY: David Reiss
Posted 9 years ago
POSTED BY: Dana DeLouis

Thanks, that's helpful. I've got the Units stuff working OK now, but I was playing around with sounds (Play, EmitSound, etc.) and had to quit and restart MMA before it would actually make noise. At one point in the process, just as with Units, it appeared that something was being loaded from the Wolfram site. On the other hand, the few Entity things that I've tried from the Help examples (e.g., Entity["Mythology"]["Properties"]) have worked OK.

How do you reset Paclet data? Via PacletUpdate, or ...?

Posted 9 years ago
POSTED BY: Dana DeLouis
POSTED BY: David Reiss

I often see this problem where units stop working but I have not been able to produce a sequence of commands to reproduce it. However, I have found this commands fixes the issue:

<<QuantityUnitsLoader`

This does not prevent the issue from hapening again in the future but at least fixes it when it happens.

POSTED BY: Gustavo Delfino
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