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Re: [ferret_users] EOF_analysis



Hi,
First to clarify, the EOF functions are internal Ferret functions, not scripts.

The EOF demo script calls all three EOF functions.  It first lists the result of the STAT function which will give you the number of eof's returned, percent variance each explains and the eigenvalues.  That output is listed here:

 
!  Compute the statistics on the EOF solution.  EOF_STAT returns:
!  for J=1  the number of EOFs returned
!  for J=2  the percent variance explained by each EOF
!  for J=3  the eigenvalue for each EOF
 
LET estat = eof_stat(sample_function, 0.1)
 
LIST/I=1/J=1 estat
             VARIABLE : EOF_STAT(SAMPLE_FUNCTION, 0.1)
             X        : 1
             Y        : 1
          441.0
 
LIST/I=1:4/J=2 estat
             VARIABLE : EOF_STAT(SAMPLE_FUNCTION, 0.1)
             SUBSET   : 4 points (X)
             Y        : 2
             2   
             2
 1   / 1:  92.10
 2   / 2:   7.90
 3   / 3:   0.00
 4   / 4:   0.00
 
LIST/I=1:4/J=3 estat
             VARIABLE : EOF_STAT(SAMPLE_FUNCTION, 0.1)
             SUBSET   : 4 points (X)
             Y        : 3
             3   
             3
 1   / 1:  2588.
 2   / 2:   222.
 3   / 3:     0.
 4   / 4:     0.
Next, after you hit RETURN, it plots the spatial variation, which is the variable defined as

let exy = EOF_SPACE(sample_function, 0.1)

Here the first eigenfunction is shown as the result at L=1, and the second eigenfunction is the result at L=2:
SET VIEW vll; CONTOUR/L=1/TITLE="EOF 1" exy  ! this is the first spatial eigenfunction
SET VIEW vlc; CONTOUR/L=2/TITLE="EOF 2" exy ! this is the second spatial eigenfunction
To save the first eigenfunction, you would save the variable exy[L=1], and  likewise the second is exy[L=2]. In the figure, the upper frames are the original function, for comparison, and the lower ones are the eigenfunctions.

eof_space.gif
Finally the script computes and plots the time amplitude functions.  The demo goes on to compute eof's using the example coads_climatology dataset.  You could do something similar using a different dataset or a different region. Call EOF_TFUNC to get the time amplitude function and EOF_SPACE to get the spatial eigenfunctions.



On 8/4/2010 2:53 AM, medepalli santha raju wrote:

Hi All,

I am ferret new learner. I have done ef_eof_demo exercise

for showing EOF modes for monthly SST over Taiwan region from 1996 to 2001.

It was giving only temporal modes. Could you please, help me.

I have following doubts:

1) How will I get spatial modes from that script (ef_eof_demo)
.
2) How will I get function scripts (EOF_SPACE, EOF_TFUNC, and EOF_STAT)

which was given in ef_eof_demo.

Thank you,

Santha Raju.


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