Vector-valued Quantities

[David Berry]

Ed,

>     Next we want to combine quantities, but we want to do this keeping
> some relationship between the index values of both quantities.  This is
> commonly the case when the nth element in each quantity refer to the
> same object.  QuantitySet provides for a standard way to get your ducks
> in a row.

Given that a CoreQ consists of a Frame and a Mapping (taking a
ValuesList to be a special form of Mapping), it is represented by:

   CoreQ {
      Frame f;
      Mapping m;
   }

Let's say we have two scalar-valued CoreQ's:

   CoreQ flux
   CoreQ wavelength;

If we then want to combine these into a single vector-valued CoreQ, do
we not just join the two Frames together to form a compound Frame,
and then joing the two Mappings together to form a compound (parallel)
Mapping, and then combined them in a new CoreQ as follows:

   CoreQ SED {
      CompoundFrame {
         flux.f
         wavelength.f
      }
      ParallelMapping {
         flux.m
         wavelength.m
      }
   }

The above *is* a CoreQ since it is made up of a Frame and a Mapping, so
why do we need a new "QuantitySet" class?

David