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 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.

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