Hi -
I'm thinking that this has to do with the context of variables in
Ferret, but I don't yet see what the answer is.
Here's a script that does the same operations, but runs faster, on
local data:
use coads_climatology
save/clobber/file=airt.nc airt
save/clobber/file=sst.nc sst
cancel data/all
use airt.nc
use sst.nc
let k2 = zcat (airt[d=1], sst[d=2])
! This is all zero's
plot k2[k=1,x=@ave,y=@ave] - k2[k=2,x=@ave,y=@ave]
save/clobber/file=k2file.nc k2
can data/all; can var/all
use k2file.nc
! This has non-zero difference
plot k2[k=1,x=@ave,y=@ave] - k2[k=2,x=@ave,y=@ave]
On 4/26/2011 12:37 PM, Brockmann Patrick wrote:
Ansley
Manke a écrit :
Hi -
I would agree; though the variables in the datsets are of type
FLOAT, so Ferret's use of single precision for variables isn't
causing a loss of accuracy in this case.
Hi,
If you plot
yes? use
"http://dods.extra.cea.fr/cgi-bin/nph-dods/data/p86denv/IPSLCM5A/PROD/rcp45/v3.rcp45.1/ATM/Analyse/TS_MO_YE/v3.rcp45.1_20060101_21651231_1Y_t2m.nc"
yes? use
"http://dods.extra.cea.fr/cgi-bin/nph-dods/data/p86denv/IPSLCM5A/PROD/rcp45/v3.rcp45.2/ATM/Analyse/TS_MO_YE/v3.rcp45.2_20060101_21001231_1Y_t2m.nc"
yes? plot/l=1:40 T2M[i=@ave,j=@ave,d=1]
yes? plot/l=1:40/over T2M[i=@ave,j=@ave,d=2]
to be compared to
let a=zcat(T2M[d=1],T2M[d=2])
plot/l=1:40 a[i=@ave,j=@ave,k=2], a[i=@ave,j=@ave,k=1]
You will see that this not an accuracy problem.
I would rather suspect the ZCAT function to be problematic.
Patrick
Ansley
On 4/26/2011 9:41 AM, Martin Schmidt wrote:
Hi Patrick,
I can reproduce your finding. I GUESS, the i/j-average of the
difference between both
the experiments is pretty small, even if there are significant
differences in some areas. The average runs over 10^4
points. The quantities are of the order 200, the difference is
less than +/-10.
Hence it may be that you see simply the limited accuracy of
ferret.
I do not know nothing about the experiments, but may it be
that some procedure has been applied to
keep the average values fixed?
Greetings,
Martin
Brockmann Patrick wrote:
Hi all,
Sorry for the uncompleted previous message.
When you analyze ensemble realizations
(read
http://cmip-pcmdi.llnl.gov/cmip5/docs/cmip5_data_reference_syntax.pdf
Ensemble menber paragraph), you would like to work with
a variable over its realizations seen as a nth dimension and
then apply on it power of ferret transformations.
Unfortunatelly, there are only 4 dimensions in ferret.
But sometimes, you also may have the chance that the
variable you analyze
has 3 dimensions and has a XZT shape.
I have imagined to use the ZCAT function to concat the XYT
variable over the Z dimension
and then get a XYZT variable with the Z dimension
representing a realization dimension.
It seems to work since for one time step I can shade a
difference but when I plot
a time evolution I get the same plot from the 2
realizations. That is not correct.
Try the attached script if interested.
Any share of experience on this topic is welcome. The
challenge of course is not
to physically save files.
Patrick
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