Fix uconvert For Inverse Units

[acdupont]

uconvert does not calculate the correct value for inverse units.

This works as expected:

julia> uconvert(u"m^3", 1000000.0u"cm^3")
1.0 m^3

When using inverse units, I expected the value 1.0 m^-3 but got this instead

julia> uconvert(u"m^-3", 1000000.0u"cm^-3")
1.0e12 m^-3

[giordano]

@briochemc this works on v1.2.0 but not v1.2.1. Looks like #335 wasn't enough

[acdupont]

hmm, I think my logic is wrong. if there are 1000000 "things" per cm^3, then there will be a magnitude more than that in a m^3, so it looks like Unitful's answer here actually is correct.

[giordano]

Also, I was testing the wrong function in the REPL 😑 The result is consistent across all versions v1, v1.1, v1.2.0, v1.2.1. @briochemc Sorry for the noise!

[giordano]

hmm, I think my logic is wrong. if there are 1000000 "things" per cm^3, then there will be a magnitude more than that in a m^3, so it looks like Unitful's answer here actually is correct.

Yes, this is a volumetric density, so if you go to a larger volume you expect "more stuff", and the factor 10^6 when going from a volume of 1cm^3 to 1m^3 looks indeed correct. Ok, I think we can close this ticket.