Hi,

Thanks for emailing me Nicolas.

I had a quick play with writing a units extension really just to learn
more about SAGE. I've only just started writing this so its still a
way off being ready for prime time but so far you can create
quantities with units, manipulate them like any other number and
convert to different units. There is also a sub-library of common
physical constants with units.

I hadn't heard of the Quantity package until just now but it looks
much more mature than what I have been working on. I took a slightly
different approach in that in my code quantities are always kept in SI
base units so simplification is never necessary but that means that
sometimes it makes assumptions about what units the user would like
the results in e.g.

(10 * meter)**3 / (5 * ft)**2

will give 40 m**3/ft**2 in Quantity as it is unclear whether the user
wants the result in meters or feet and the user must explicitly
simplify the result to the unit they wanted, whereas in my code will
always output in meters and the user can convert it to feet if needed.
This also means you can add dissimilar units of the same
dimensionality and the result will just end up in SI units.

I will clean up my code and make a little demo so people can play with
it when I have a bit more free time on tuesday, if anyone is
interested. I'm still keen to keep developing my implementation but I
can see that porting Quantity to work with SAGE might be a quicker way
to get a mature units system up and running.

Thanks,
Fergus

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