Unexpected results when dealing with unitless quantities (dividing quantities in an unsual orders) #94
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JoshuaCapel
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christianp
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Dec 3, 2018
Aims to fix gentooboontoo#94. The method to multiply q1 by q2 goes as follows: * if q1 and q2 are compatible (they have exactly the same signature), convert q2 to the same units as q1 * collect together the numerators and denominators of q1 and q2, and 'clean' * multiply q1 and q2's scalars together, and return a unit that big with the cleaned numerator and denominator The cleaning code doesn't gather together units of the same kind, but with different prefixes. I suspect this is deliberate, but it leads to inconsistencies like Qty('1 m').div('1 km') = 0.001, but Qty('1 m').mul('1 1/km') = 1 m/km. This commit changes `cleanTerms` to keep track of the prefix used with each unit, and accumulate a scaling factor when the same unit is used with a different prefix. The function returns numerator, denominator, and the scaling factor. Following the logic that 'km*m' returns a quantity in km, and 'm*km' returns a quantity in m, the prefix associated with the first occurrence of each unit encountered is used.
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Thanks for reporting, your expectations are right and resulting units were inconsistent. |
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If I calculate
Qty("1m").div("1km")I get a unitless 0.001 as I expected.But if I calculate
(Qty("1").div("1km")).mul("m")I get 1 m/km. Which is actually correct, but I would have expected this to just be a unitless 0.001 as above.Also if I calculate
(Qty("1").div("1km")).mul("m").mul("")I get 0.001 m2/km2. Again this is technically the correct result, but not what I would have expected.Is this an issue with js-quantities, or are my expectations wrong?
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