Re: SAVE in EOF analysis

[Sim Larkin <larkin@xxxxxxxxx>]

Boyin -

Your 120E:70W / 40s:50n domain contains
~85 points in the X dimension
~45 points in the Y dimension
for a total of 85*45 = 3825 grid cells

This means the EOF routine has to diagonalize a 3825 x 3825 square matrix
containing >14 million cells.

Most exact diagonalization routines (such as used by FERRET) perform order
(matrix dimension)^3 number of iterations to solve.
In your example, your computer has to do order(55 billion) matrix
operations to solve it (each matrix operation = many computer cycles and
generally uses random memory access also slowing things down).

I would be surprised if such calculations able to be done in a reasonable
time.

Many large matrix diagonalization calculations in the past have used
inexact approximations that greatly limit the number of iterations
required.
I don't know of any coded routines for this, but perhaps some other Ferret
User does.

- Sim



-------------------------------------------------------------------------------------------------

Sim Larkin
Research Physical Climatologist, AirFIRE Team
USDA Forest Service Pacific Wildland Fire Sciences Laboratory
400 N. 34th St Suite#201, Seattle, WA 98103
Email: larkin@fs.fed.us
206.732.7849
-------------------------------------------------------------------------------------------------


|---------+--------------------------------------->
|         |           Boyin Huang                 |
|         |           <huang_boyin@yahoo.com>     |
|         |           Sent by:                    |
|         |           owner-ferret_users@ferret.pm|
|         |           el.noaa.gov                 |
|         |                                       |
|         |                                       |
|         |           09/25/2003 01:40 PM         |
|         |           Please respond to byh       |
|         |                                       |
|---------+--------------------------------------->
  >--------------------------------------------------------------------------------------------------------------------------------------------------|
  |                                                                                                                                                  |
  |        To:      ferret_users@ferret.wrc.noaa.gov                                                                                                 |
  |        cc:                                                                                                                                       |
  |        Subject: SAVE in EOF analysis                                                                                                             |
  >--------------------------------------------------------------------------------------------------------------------------------------------------|




Hi, ferreters:

Is the ferret so slow in doing EOF analysis?

Using the demo file for eof analysis:

-------------------------------------------------------
SET REGION/X=67w:1w/Y=11S:11N
USE coads_climatology
LET eof_xyfcn = eof_space(sst, 0.5)
SAVE/CLOBBER/FILE=sst_clim_eof_space.cdf eof_xyfcn

USE sst_clim_eof_space.cdf
SET VIEW ul; fill/l=1/TITLE="eof 1" eof_xyfcn; go land
-------------------------------------------------------

Which works fine to me. Now I wish to have EOF in a
larger domain, say 120E-70W and 40S-50N.

I replaced set region by
SET REGION/X=120e:70w/Y=40S:50N
and added
SET MEMORY/SIZE=260.(my computer memory is 1.5gb).

I found that the ferret runs for ever (how long should
I wait for?).

I tried to diagnose the problem by typing these
command lines interactively line by line, and found
the problem is that the program was stuck by SAVE
command.

I then tried NOT to use the save command, but ferret
says that the variable was not found.

So, do we have to save EOF first, and the read and
plot?

How can I do the EOF analysis within a larger space
domain and long time series? Say, simulated global SST
with 200x100 grids for 1200 month, sst(200,100,1200).



=====
Boyin Huang
The Center for Research on the Changing Earth System (CRCES)
10211 Wincopin Circle, Suite 240
Columbia, Maryland 21044
Tel. 410-992-5300/819 (O), 410-737-4557(H)
Fax. 410-992-5944, Email. byh@crces.org
http://byh.crces.org

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