Numerical reproducibility: netcdf vs. pnetcdf

[John Michalakes]

I'm comparing WRF output using regular Netcdf 3.6.0 against the new output
that generated using pNetCDF, and for all but one fields it comes out bit
for bit the same. Curiously, one field is not comparing bit for bit, but the
differences are very small relative to the size of the values -- possibly
within a low order bit of each other (though I haven't looked at it
carefully enough to be sure of that).

I've been working under the assumption that output generated using NetCDF
and pNetCDF should compare bit for bit. Is that a reasonable assumption, or
might there be differences in versions that could lead to slight different
(within roundoff) output for certain ranges of values? Perhaps this is a
question for Unidata too.

Can you tell me please what version of NetCDF that pNetCDF is based on?

Thanks,

John

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John Michalakes, Software Engineer        michalak at ucar.edu
NCAR, MMM Division                   voice: +1 303 497 8199
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        http://www.mmm.ucar.edu/individual/michalakes
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