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Would it be possible to get Mathematica to group units more sanely. For example the calculation:

m = Quantity["Meters"];
D[
  D[
   Sin[p] (m),
   Quantity[p, "Seconds"]] ,
  Quantity[p, "Seconds"]] // Expand

This gives an visual output:

(-1 m/s^2) Sin[p]

however it would be more natural to show:

 -Sin[p](m/s^2)

I there a way to make this happen.

Notes:

  • Expand is strictly not necessary in this case but can nice be in more complex cases.
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1 Answer 1

Reset to default
2
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These seem to work

m = Quantity[#, "Meters"] &;
D[D[Sin[p] // m, Quantity[p, "Seconds"]], 
  Quantity[p, "Seconds"]] // Expand

Or you transform by hand

nonQuantitiesAsMagnitudes[expr_] := 
 expr /. x_ Quantity[y_, unit_] :> Quantity[x y, unit]

m = Quantity["Meters"];
D[
  D[
   Sin[p] (m),
   Quantity[p, "Seconds"]] ,
  Quantity[p, "Seconds"]] // Expand //nonQuantitiesAsMagnitudes
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  • 1
    $\begingroup$ Yeah that's it. Still think that Mathematicas syntax for units is atrocious. My engineering students seem to come up with hives about this. But i think they can live with this. What does the &; do? $\endgroup$
    – joojaa
    Commented Jan 13, 2014 at 19:25
  • $\begingroup$ Terribly late reply, but & makes the preceding term into a pure function, while the ; ends the statement and suppresses output. This means you can use m as a function, where # represents the first argument: m[1] would evaluate to Quantity[1,"Meters"]. The // in the second line is a postfix function application, so the m is used as m[Sin[p]]. $\endgroup$
    – Widjet
    Commented Mar 9, 2015 at 6:03

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