Re: calculating standard deviation of a grid

On Fri, 2007-06-01 at 12:26 -0400, Case.Jon wrote:
> Dear Gembud,
>  
> Does anyone know of a way to calculate the standard deviation of a specific 
> grid using GDLIST?  
> There is a function to give you the average of a scalar grid over the GAREA, 
> but I don't see a way to specify a GFUNC that can calculate the standard 
> deviation.  
>  
> Actually, the only missing link I need is to find the number of non-missing 
> grid points in the array.  I haven't identified such a utility though.  

Jon,

You can determine the number of non-missing grid points in your sub
area 
using a function like:
GDPFUN   = ysum(xsum(bool(S)))

The bool(S) function will provide a 1/0 output with 1's at existing
points, so
the column sumation of the individual row sums will produce a grid of
the number of non-missing points at all points. You could further assign
the
value to just the non-missing point locations (but not needed here)
with:
GDPFUN = mask(ysum(xsum(bool(S))),S)

The standard deviation of the grid area could be done in GDPLOT2 similar
to:
GDPFUN = 
ysum(xsum(bool(tmpc)))//n!mul(savs(tmpc),n)//sm!mul(savs(expi(tmpc,2)),n)//ss!sqrt(quo(sub(ss,quo(mul(sm,sm),n)),sub(n,1))
(or the individual terms above can be computed in GDDIAG to output with
GDLIST).

Steve Chiswell
Unidata User Support





>  
> Also, I've looked at the GDSTAT program, but that give you statistics at each 
> individual grid point over a range of times, not stats for a while grid.
>  
> Your feedback is most welcome!
> Jonathan
> 
> ......................................................................The 
> information contained in this email message is intended only for the use of 
> the individuals to whom it isaddressed and may contain information that is 
> privileged and sensitive. If the reader of this message is notthe intended 
> recipient, you are hereby notified that any dissemination, distribution or 
> copying of thiscommunication is strictly prohibited. If you have received 
> this communication in error, please notify thesender immediately by email at 
> the above referenced address. Thank you.
> 
> ===============================================================================
> To unsubscribe gembud, visit:
> http://www.unidata.ucar.edu/mailing-list-delete-form.html
> ===============================================================================
-- 
Steve Chiswell <address@hidden>
Unidata