issues with unit package

• To: mathgroup at smc.vnet.net
• Subject: [mg88634] issues with unit package
• From: Jay Ortiz <omaha8master at yahoo.com>
• Date: Sat, 10 May 2008 06:54:10 -0400 (EDT)

```Why won't Mathematica when using the Units package eliminate reciprocal units?   Consider an example from E&M, finding the wavelength corresponding to a frequency:

<<Units`
<<PhysicalConstants`

In[1]:=
Freq=100*^6 Hertz;
Wavelength=SpeedOfLight/Freq
Out[1]=(149896229*Meter)/(50000000*Hertz*Second)
In[2]:=N[Wavelength]
Out[2]=(0.299792*Meter)/(Hertz*Second)

i.e. Mathematica doesn't know that Meter/(Hertz Second) should reduce to Meter.   Shouldn't this be handled?

Another example; shouldn't Mathematica reduce expressions in consistent units to a single result?    Example:

In[5]:=3 Ohm + 1 Volt/Ampere
Out[5] =  3 Ohm + 1 Volt/Ampere

Why not 4 Ohm, or 4 Volt/Ampere?   After all, the documentation entry for Ohm says it's equivalent to Volt / Ampere, so it's reasonable that Mathematica would be aware of that relationship.  Doing SI[] or MKS[] on those expressions doesn't change anything.

Maybe the Units package doesn't extend to manipulating variables with quantities that have units.  Am I missing something here?

Thanks.

```

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