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Re: Computing Derivatives



On Mon, 14 Mar 2005, Steve Guimond wrote:

>    I need to compute vorticity over a certain domain and want to know the
> best way to do this in ferret.

Hi Steve,
	If you look at the transformations in the Ferret user manual you
will find @ddc, @ddf, and @ddb which perform central, forward, and
backward derivatives. They have another benefit too in that if your data
are on a latitude-longitude grid, and the axes are properly set up with
units in degrees, the results will be in "per meter" and in the case of
zonal derivatives the cosine latitude will be built in. So you'd
probably use something like
	let vorticity=v[x=@ddc] - u[y=@ddc]
for relative vorticity.
	Some other relevant info can be found by searching for
"derivatives" in the on-line mail archives of the user group

http://ferret.wrc.noaa.gov/Ferret/Mail_Archives/ferret_mail_archives.html

There is not a lot under "vorticity" although the question has come up
a number of times. Perhaps users who get suggestions privately could
conclude the mail threads with a summary e-mail about what ultimately
worked best for them.

Good luck,
Mick


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