[ferret_users] precision problem on a difference between a same variable read from 2 files with the same structure

[Patrick Brockmann <patrick.brockmann@xxxxxxxxxxxx>]

Hi ferreters,

I encountered a problem when I compare a variable

read from 2 different files with exactly the same structure (same axis in particular).

The difference calculated with ferret has the following range: 

   Minimum value: -2.1516798E-11

   Maximum value: 2.15167981E-11

but the difference calculated with ncdiff has  the following range: 

   Minimum value: -2.79521E-20

   Maximum value: 2.87991E-20

--> I was expecting the same order of magnitude with ferret than with ncdiff.

More strange, if I change the name of a coordinate axis of one of the input file

then the difference calculated with ferret and ncdiff have the same order

of magnitude.

--> I suspect that the variable read from the 2nd file uses a downward axis

set from the read of the 1st file.

Attached the minimized problem with 3 small nc files and 2 test scripts.

Please try:

$ ferret -script test1.jnl

$ ferret -script test2.jnl

Tested with ferret 7.44 and 7.50

Any help welcome.

Regards

Patrick

--
Data Analysis and Visualization Engineer / Project Manager
LSCE/IPSL, CEA-CNRS-UVSQ laboratory
LSCE - Climate and Environment Sciences Laboratory
IPSL - Institut Pierre Simon Laplace
--

Attachment: ci_restart_extract.nc
Description: Cdf file

Attachment: diff.nc
Description: Cdf file

Attachment: err1.jnl
Description: Binary data

Attachment: err2.jnl
Description: Binary data

Attachment: run_restart_extract.nc
Description: Cdf file

Attachment: run_restart_extract_renamed.nc
Description: Cdf file