Underflow problem on NEC SX-4 in Cray-compatible mode

• To: netcdfgroup <netcdfgroup@xxxxxxxxxxxxxxxx>
• Subject: Underflow problem on NEC SX-4 in Cray-compatible mode
• From: Harvey DAVIES <hld@xxxxxxxxxxxx>
• Date: Tue, 24 Feb 1998 14:57:25 +1100 (EST)

The problem occurs in Cray (float2) mode when calling a netCDF put routine.
On the NEC SX, netCDF converts from Cray to IEEE floating point by calling the
NEC function fl2_ie3 from various places in src/libsrc/ncx.c.  Underflow is
possible because the Cray format has more exponent bits. Each underflow
generates the (normally) desired value of 0, but does not increment the
function result, which is a count of correct conversions.  E.g. 3 underflows
in a vector of 8 elements would give a result of 5.  NetCDF detects the fact
that this result is less than expected & generates error -60.  There appears
to be no way of modifying the behaviour of fl2_ie3 to count underflows as
normal conversions.

One solution would be to count the values small enough in magnitude to
underflow before calling fl2_ie3.  However, I suspect this would be too costly
in time to be worthwhile.  So (unless I am being too pessimistic here and
Glenn Davis implements some such solution in ncx.c) the user should anticipate
the possibility of error -60 occuring in put routines.

Harvey Davies, CSIRO Mathematical and Information Sciences,
Email: harvey.davies@xxxxxxxxxxxxx
Phone: +61 3 9669 8110 or +61 3 9239 4556
  Fax: +61 3 9669 8112


>From owner-netcdfgroup@xxxxxxxxxxxxxxxx Mon 9  1998 Mar 15:15:31
Date: Mon,  9 Mar 1998 15:15:31 -0500
From: Fred Knight <knight@xxxxxxxxxx>
To: netcdfgroup@xxxxxxxxxxxxxxxx
Subject: request: plotting utility
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Reply-To: Fred Knight <knight@xxxxxxxxxx>

I want to browse a netCDF file and be able to make plots.

I have a utility written by a summer student at NCAR.  It runs under
IDL, is called ncbrowse, works fairly well, and is an aid to seeing what
is in a netCDF file.  It also requires IDL and doesn't plot one vector
wrt another vector.

So I'm looking for a Unix utility with X interface to browse a netCDF
file and plot variables, including one vector (unlimited or otherwise)
with another.  I'd appreciate any leads.

Thanks, Fred

-- 
Fred Knight | knight@xxxxxxxxxx | 781 981 1053 | fax: 781 981 5359
C-490 | MIT Lincoln Laboratory | 244 Wood Street | Lexington, MA  02173