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Comment Concerning Derivatives

Hello Ferret World,

With the help of Mick Spillane , I was able to "ferret" out a solution
to my derivative problems (Mick, jump in if I get some of the
terminology botched on this).  If you recall, I was computing the
vertical component of vorticity on a sphere, namely using:

 Vort=(vwnd[x=@ddc]-uwnd[y=@ddc]+(uwnd/r)*tan(y*d2r)) (note, d2r is
degrees to radians variable)

Yet my hand calculated values were not matching ferret's values.  Why?
Because I was assuming that the abstract variables x, y, t were
automatically assigned to the Pseudovariables on my netcdf file.
However, I must first tell ferret that x, y, and t are associated with
axis used by the cdf file, or I won't get correct values.  I got around
this problem by just using some of the defined variables and commands in
my script to take care of this:

list /x=170e/y=20s sin(y[g=u]*d2r), cos(x[g=u]*d2r)

Note that I am telling y and x to be associated with the axis given to
my variable "u" ( the x[g=u], y[g=u] parts in the trig terms) located
within my netcdf file.  Once this was done, all of ferret's values
matched my hand calculations.  This may be apparent to most folks
already, but if this wasn't hopefully this info will help.


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