Converts degrees Celcius to Kelvins without prompting

Questions
1

Using version 13.2, Mathematica converts degrees Celcius to Kelvins without prompting:

{4*Quantity[20, "DegreesCelsius"], C -> Quantity[1,  "Kilojoules"]/(Quantity[1, "Kilograms"] Quantity[1, "DegreesCelsius"])}

{Quantity[5863/5, "Kelvins"], C -> Quantity[20/5483, ("Kilojoules")/("Kelvins" "Kilograms")]}

This is certainly not correct.
Regards,
Sinval

2

I’m not seeing any conversion happening for those expressions. What were you expecting to see?

3

Hello, Eric.
I am sending, in attachment, a simple notebook.

example1.nb (3.28 KB)

4

Well, we need more information on how you got to that state. If I execute the cell in that notebook the output uses Celsius, i.e. no conversion. I don’t know how the original output was generated, but I cannot reproduce any implicit conversions with what you’ve provided so far.

5

In my notebook, I entered the units using the Quantity function or the Ctrl + = keys. Look again at the attached notebook.

example1.nb (5.8 KB)

6

I tried using Ctrl+= as well as Quantity. I get no implicit conversions. And again, if I evaluate your cells in place, I do not get the outputs you had in there originally.

I also notice that your outputs are actually wrong in the sense that if a conversion had occurred, it’s faulty (which seems even worse than implicit conversion itself). Specifically, 80 degrees celcius is closer to 350 kelvins than to the over 1100 kelvins that appears in your notebook.

So, my first suspicion is that there were some previous calculations that you haven’t shown us that set up some variables or functions that are being applied in these expressions. (You could test this by killing and restarting the kernel.)

If that’s not it, then maybe there is some setting/preference that is set differently in your environment than in mine. Maybe there are options for automatically converting certain units. Seems unlikely, but I’m just brainstorming here.

7

I can reproduce what Sinval reports. From his attached notebook:

In version 12.3

Celsius12.3.png

In Version 13.2

Celsius13.2.png
Celsius13.2.png384×109 2.39 KB

I am using Windows 11

8

There were no previous calculations. If I restart Mathematica and create a new notebook (starting from scratch) the problem remains.

9

Thanks Hans for the contribution. Version 13.1 didn’t have this problem; appeared in 13.2

10

Based on Hans’ comment, it sounds like it’s either version dependent or OS dependent. I’m running Mathematica version 13.1 on MacOS 12.6

11

I’m running Mathematica version 13.2 on Windows 11.

12

It makes no sense to multiply a Celsius temperature by a coefficient. Version 13.2 has introduced temperature differences, and the behaviour in such situations has changed. The unexpected output happens on MacOS 13.1 with just this input:

4*Quantity[20, "DegreesCelsius"]

With Mathematica 13.2 try this instead:

4*Quantity[20, "DegreesCelsiusDifference"]
13

Good point. I was so focused on not being able to reproduce the behavior that I didn’t even think about the semantics. I’ve even run into this before and wondered why sometimes it seems like Quantity units are treated like arbitrary tags. It’s almost like you could do Quantity[4, abc] and have subsequent operations just treat abc like a formal variable or something. But anyway, kind of nice that MMA does “the right thing” in the update.

14

I am grateful for the information, Gianluca and Eric. I will check the modifications contained in version 13.2 and adapt my notebook.

Regards,

Sinval

15

Sorry, I meant 4*Quantity[20, "DegreesCelsius"] in MMA 13.2: it gives the same output as

UnitConvert[Quantity[20, "DegreesCelsius"], "Kelvins"]*4

Kelvin degrees can be multiplied by a number.

16

Thanks again for your attention Gianluca.