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Programs for reading and writing parallel NetCDF files


A Parallel I/O Library for NetCDF File Access


Parallel I/O Library for NetCDF File Access (openmpi version)


ncmpidiff - compares two netCDF files in parallel


mpiexec -n np ncmpidiff [-b] [-q] [-h] [-v var1,...,varn] [-t diff,ratio] file1 file2


ncmpidiff runs in parallel on np number of MPI processes to compare the contents of the two files and reports the first difference to the standard output.
For variables and attributes, it reports the array indices of the first element found different when option -t is not used. When option -t is used, it reports the element with the largest difference that fails to meet the tolerance requirements.
If neither argument -v nor -h is given besides the two file names, the entire files are compared.
When comparing two files entirely, the difference between ncmpidiff and the Unix command diff is that ncmpidiff skips the gaps between variables. The gaps may occur when the alignment feature is used to create a new file. This alignment allows to allocate a larger space for the file header and align the starting file offsets of fixed-size variables (see API ncmpi__enddef and PnetCDF hints). Oftentimes, the contents of gaps are non-zero arbitrary bytes. Thus, two netCDF files (of same or different sizes) can be reported identical by ncmpidiff but not by diff.


-b Verbose mode - print results (same or different) for all components (file, header, or variables) in comparison
-q Quiet mode - print nothing on the command-line output. This also disables verbose mode. When in quiet mode, users should check exit status. See below in "EXIT STATUS".
-h Compare file header only
-v var1,...,varn Compare only the given list of variables (names separated by comma without space).
-t diff,ratio Compare variables element-wisely with tolerance (diff and ratio separated by comma without space). diff is the absolute value of element-wise difference of any two variables. ratio is the relative element-wise ratio, for instance, MAX(x,y) / MIN(x,y) - 1, where x is an array element from a variable in the first file and y is the corresponding array element of the same variable in the second file. Note when this option is used, the comparison will compare the entire variables and reports the element with the largest difference that fails to meet the both tolerance requirements.


An exit status of 0 means no differences were found, and 1 means some differences were found. Note on VMS-based system, the exit status values are reversed.


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