NAME

       ncmpidiff - compares two netCDF files in parallel

SYNOPSIS

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

DESCRIPTION

       ncmpidiff runs in parallel on np number of MPI processes to compare the contents of the two files and re‐
       ports the first difference to the standard output.

       For  variables and attributes, it reports the array indices of the first element found different when op‐
       tion -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 cre‐
       ate a new file. This alignment allows to allocate a larger space for the file header and align the start‐
       ing file offsets of fixed-size variables (see API ncmpi__enddef and PnetCDF hints). Oftentimes, the  con‐
       tents  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.

OPTIONS

       -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  two variables with  the  same  name  but
              stored  in the two input files.  ratio is the relative element-wise difference ratio defined as |x
              - y|/max(|x|, |y|), 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. |x| represents the absolute
              value of x. Note when this option is used, the output reports only the first  array  element  that
              fails to meet both tolerance requirements.

EXIT STATUS

       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.

SEE ALSO

       ncmpidump(1), cdfdiff(1), diff(1), pnetcdf(3)

DATE

       February 21, 2022

Printed: 2025-07-18                              PnetCDF 1.12.3                                     ncmpidiff(1)