problem of the extenal function -- lsl_lowpass

[alutw <alutw@xxxxxxxxxxxx>]

Hi all: 
 I got a problem for using lsl_lowpass function to 
filter my 2D  daily data. 

My dataset and varibles as following 

=============================================================================
   1> ./st.cdf  (default) 
name     title                             I        J        K         L 
SALTC    Salinity on z-level              1:160    1:70      1:12      1:1826 
TEMPC    Temperature on z-level           1:160    1:70      1:12      1:1826 
=============================================================================
    TTW20 = TEMPC[I=70:120,J=1:50,K=3] 
    LP20 = LSL_LOWPASS(TTW20,365,365) 
=============================================================================

While i shaded lp20 , " command : "yes? shade/l=10 lp20" , 
I got  error message as following : 

=============================================================================
Bailing out of external function 
"lsl_lowpass": 
       LSL_FILTER: The filter span must be less than or equal to the number 
of points 
**ERROR: : error in external function 
=============================================================================

Actually,I have no idea where I went wrong. 
I'd like to know how the lsl_lowpass function to be apply for 2D or 3D data. 

Teach me to solve this problem,plz. 
Sorry for my poor English. 
Thanks a lot. 


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