[ferret_users] axis and average 'problems'

[Izidine Pinto <izidinep@xxxxxxxxx>]

Dear ferret users

This might be  basic but I'm having problems. 
I have a file which I would like to define a time axis, select a time/rergin of interest and average. 




 sh d
     currently SET data sets:
    1>AFRICA_GPCC_CTL_GPCC5_MM_50km_1981-2009_pr.nc  (default)
 name     title                             I         J         K         L
 LON      longitude                        1:194     1:201     ...       ...



 LAT      latitude                         1:194     1:201     ...       ...
 TIME                                      ...       ...       ...       1:349
       (invalid coordinate axis)
 PR       Precipitation                    1:194     1:201     ...       1:349



yes? sh axis time
 name       axis              # pts   start                end



 TIME                         349 r   1                    349
   Axis span (to cell edges) = 349



yes? show data/attr
(time)                 DOUBLE    units           CHAR        30   T       days since 1950-01-01 00:00:00



                                 calendar        CHAR        8    T       standard
                                 orig_file_axnameCHAR        4    F       time



This is how I defined the axis
yes? DEFINE AXIS/T="15-JAN-1981:00:00":"15-DEC-2009:00:00":1/T0=01-JAN-1950:00:00:00/units=months/calendar=360_day/modulo tmonth



yes? DEFINE AXIS/X=-24.64:60.28:0.44/UNIT=DEGREE xlong
yes? DEFINE AXIS/Y=-45.64:42.24:0.44/UNIT=DEGREE ylat



yes? DEFINE GRID/X=xlong/Y=ylat/T=tmonth newgrid
yes? let PR_rg=PR[d=1,g=newgrid@asn]



For example the results of 
PR_rg[l=1:3@ave] 
and
PR_rg[T="15-JAN-1981":"15-MAR-1981"@ave]



are different. 
Could anyone help me to understand why is this happening? And what would be the limit of  T equal to L.

Thanks in advance.



-- 




Izidine S. Pinto