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Hi - The function expects an xyt grid; and if the variable also has a Z coordinate, it computes the EOF at each z level. You could do the computation in xyz, if you define a grid which is x,y and t, where the time axis is the same length as your z axis, and regrid your data to that new xyz grid with the RESHAPE regridding transformation. Ansley Jian Ma wrote: Hi Ansley and All, In the EOF Demo, it is said that the input data may be a function of z. What does it mean? Say if I have my data on x,y,z only, can I do the EOF mimicking the z coordinate as "time"? Many thanks, Tony On Fri, 2009-07-10 at 09:48 -0700, Ansley Manke wrote:Hi Xia, The script ef_eof_demo.jnl is contained in the fer_environment.tar file from the Ferret downloads pages, so if you have installed Ferret it should be available in your scripts directory. I will copy it below for you as well. We also have an html version of this demo, which can be found under the "tutorials" link on the Ferret documentation page. http://ferret.pmel.noaa.gov/FERRET_17sep07/Demos/ef_eof_demo/ef_eof_demo.html \SET MODE VERIFY ! ef_eof_demo.jnl ( acm 9/2000) ! Description: Demonstration of computing EOFs using the ! External Functions EOF_SPACE, EOF_TFUNC, EOF_STAT ! The functions implements Chelton's '82 method for finding EOFs of gappy ! time series. All the functions perform the same computation but return ! different portions of the results. ! * EOF_SPACE returns EOF eigenvectors: spatial EOF in x and y with the ! same units as the incoming data ! * EOF_TFUNC returns EOF time amplitude functions; dimensionless ! * EOF_STAT returns statistics on the EOF computation: number of EOFs ! scaled and returned; Percent variance explained by each EOF; and the ! eigenvalues. ! ! For all functions the arguments are as follows: ! ! * 1st argument: Input data field, a function of x, y, and time; may be a ! function of z ! * 2nd argument: The minimum percent variance explained by the EOF's that ! are computed and scaled, e.g. to return EOFs that explain at least 2% ! variance, use 2.0 ! * 3nd argument: The fraction of each time series that must be present to ! include it in the calculations, e.g. to use all time series that have ! at least half the data present, use 0.5 ! ! ! EOF functions Example 1: define a function of x,y,time using trig ! functions. Decompose into spatial and time EOF's and display statistics. ! PAUSE LET time = t[t=1-jan-1990:10-jan-1990:24] ! 24 hour resolution time axis DEFINE AXIS/x=0:10:0.5 x10 DEFINE AXIS/y=0:10:0.5 y10 DEFINE GRID/x=x10/y=y10/t=time g10x10 SET GRID g10x10 LET fcn1 = 15.* sin(omega1*t)*cos(r)/(r+1) LET fcn2 = 20.* sin(omega2*t)*(sin(s)-.2*sin(q))/(s+1) LET r = ((6.*(xpts-x0)^2 + 7.*(ypts-y0)^2)^0.5) LET s = (((xpts-x1)^2 + 2*(ypts-y1)^2)^0.5) LET q = ((3*(xpts-x0)^2 + (ypts-y1)^2)^0.5) LET x0 = 2 LET y0 = 4 LET x1 = 5 LET y1 = 7 LET omega1 = 1/10*2*3.14159 LET omega2 = 2 * omega1 LET sample_function = fcn1 + fcn2 LET xpts = x LET ypts = y ! 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 LIST/I=1:4/J=2 estat LIST/I=1:4/J=3 estat ! Plot the original function (averaged over time) and its spatial ! decomposition by EOF_SPACE PAUSE DEFINE VIEW/xlim=0.,.33/ylim=.6,1./text=0.2 vul DEFINE VIEW/xlim=.33,.66/ylim=.6,1./text=0.2 vuc DEFINE VIEW/xlim=.66,1./ylim=.6,1./text=0.2 vur DEFINE VIEW/xlim=0.,.33/ylim=.1,.5/text=0.2 vll DEFINE VIEW/xlim=.33,.66/ylim=.1,.5/text=0.2 vlc DEFINE VIEW/xlim=.66,1./ylim=.1,.5/text=0.2 vlr SET VIEW vul; CONTOUR/TITLE="FCN1" fcn1[l=1:10@ave] SET VIEW vuc; CONTOUR/TITLE="FCN2" fcn2[l=1:10@ave] SET VIEW vur; CONTOUR/TITLE="FCN1 + FCN2" sample_function[l=1:10@ave] LET exy = eof_space(sample_function, 0.1) SET VIEW vll; CONTOUR/L=1/TITLE="EOF 1" exy SET VIEW vlc; CONTOUR/L=2/TITLE="EOF 2" exy PAUSE CANCEL VIEW ! Now plot the time amplitude functions. LET etim = eof_tfunc(sample_function, 0.1) SET VIEW ul PLOT/I=1/TITLE=taf1 etim SET VIEW ur PLOT/I=2/TITLE=taf2 etim ! should be all bad flags... SET VIEW ll PLOT/I=3/TITLE=taf3 etim PAUSE CANCEL DATA/ALL CANCEL VARIABLE/ALL CANCEL REGION CANCEL VIEW ! A second example, using the COADS climatology data. ! USE coads_climatology SET REGION/X=67w:1w/Y=11S:11N ! Compute and save the spatial EOF functions. These have the same units ! as the data. LET eof_xyfcn = eof_space(sst, 0.5) SAVE/CLOBBER/FILE=sst_clim_eof_space.cdf eof_xyfcn CANCEL DATA/ALL CANCEL VARIABLE/ALL CANCEL REGION USE sst_clim_eof_space.cdf SET VIEW ul; fill/l=1/TITLE="eof 1" eof_xyfcn; go land SET VIEW ur; fill/l=2/TITLE="eof 2" eof_xyfcn; go land SET VIEW ll; fill/l=3/TITLE="eof 3" eof_xyfcn; go land PAUSE CANCEL DATA/ALL CANCEL VARIABLE/ALL CANCEL REGION ! Compute the statistics on the EOFs: number of EOFs scaled ! and returned; Percent variance explained by each EOF; and the ! eigenvalues. USE coads_climatology SET REGION/X=67w:1w/Y=11S:11N LET eofstat = eof_stat(sst[X=67w:1w,Y=11S:11N], 0.5) LET nout = eofstat[i=1,j=1] LET pcts = eofstat[i=1:`nout`,j=2] LET eigenv = eofstat[i=1:`nout`,j=3] LIST nout LIST/I=1:6 pcts LIST/I=1:6 eigenv PAUSE ! Compute and save time amplitude functions: Note they are dimensionless. USE coads_climatology LET eoftime = eof_tfunc(sst[X=67w:1w,Y=11S:11N], 0.5) SAVE/CLOBBER/FILE=sst_clim_eof_tfunc.cdf eoftime[i=1:`nout`] CANCEL VIEW CANCEL VARIABLE/ALL USE sst_clim_eof_tfunc.cdf SET VIEW ul PLOT/I=1/TITLE="time function 1"/VLIMITS=-2:2:0.5 eoftime SET VIEW ur PLOT/I=2/TITLE="time function 2"/VLIMITS=-2:2:0.5 eoftime SET VIEW ll PLOT/I=3/TITLE="time function 3"/VLIMITS=-2:2:0.5 eoftime \SET MODE/LAST VERIFY Changshui Xia wrote: |