Re: ncdigest V1 #419
Harvey DAVIES (hld@dit.csiro.au)
Thu, 7 Aug 1997 14:57:51 +1000 (EST)
On Fri, 1 Aug 1997 owner-ncdigest@unidata.ucar.edu wrote:
> ncdigest Friday, 1 August 1997 Volume 01 : Number 419
> From: jps@gfdl.gov (John Sheldon)
> Date: Fri, 1 Aug 1997 19:39:29 -0400 (EDT)
> Subject: Re: More Songs about Coordinate Systems and Buildings
> > 8. correlations, using a dimension more than once:
> > precip(time, npoints)
> > precip.correlation( npoints, npoints)
> > lat(npoints)
> > lon(npoints)
>
> Your solution:
> > - will need some notation not yet formally proposed, eg:
> > :coordinates = "lat(npoints,) lon(npoints,) lat(,npoints)
> My solution:
> Not applicable..."correlation" does not possess "coordinates" the
> way we think of them. [rest deleted]
I just want to emphasise my agreement by pointing out that one could
equally well be considering correlations between different variables at
the same station. This is a little nasty in that you need a data matrix
with different units of measure for each column! E.g. say we have matrix
data(time,var)
where
var=0 is annual precipitation,
var=1 is annual mean temperature,
var=2 is annual mean relative-humidity,
etc.
Then corr(var,var) is correlation matrix.
So corr(0,2) is correlation between variables:
1. annual precipitation
and
2. annual mean relative-humidity.
You could even combine both stations and variables. E.g. start with data array
data(time,var,station)
and calculate 4D correlation array corr(var,station,var,station).
So corr(0,5,2,9) is correlation between variables:
1. annual precipitation at station 5
and
2. annual mean relative-humidity at station 9.
