# Vector-valued Quantities

David Berry dsb at ast.man.ac.uk
Thu May 13 09:32:32 PDT 2004

```Ed,

>     You don't need a QuantitySet for what you describe here.  That is
> just an SED with an alternate axis.  And I mentioned that an SED is just
> a Quantity.  You need the set when you combine luminosity and mass for a
> list of stars.

I can't see any difference between the (luminosity+mass) case and the
(flux+wavelength) case.  As before, what's wrong with a normal CoreQ in
which the the values are vectors consisting of two numbers - the flux, and
the associated mass?

CoreQ {
CompoundFrame {
LuminosityFrame
MassFrame
}
ParallelMapping {
LuminosityValue
MassValue
}
}

David

Or for flux and dust extinction along lines of sight.
>
> Ed
>
>
> David Berry wrote:
>
> >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
> >
> >
> >
> >
>
>

----------------------------------------------------------------------
Dr David S. Berry    (dsb at ast.man.ac.uk)

STARLINK project		 |	Centre for Astrophysics
(http://www.starlink.ac.uk/)	 |	University of Central Lancashire
Rutherford Appleton Laboratory	 |	PRESTON
DIDCOT				 |	United Kingdom
United Kingdom			 |	PR1 2HE
OX11 0QX                                Tel. 01772 893733
01257 273192

```