[gradsusr] grads2.1.a1 bug?

[Clark, Douglas B.]

Semyon,

I think you are getting the missing (undefined) data value of -9.99e+08 and I assume that GrADS is avoiding dividing by a small number that could potentially cause the result to overflow. But 1e-8 is a rather conservative choice for a threshold beyond which the calculation is aborted.

I think GrADS started behaving in this more conservative way sometime around v2.0 (roughly). I have got used to scaling any expressions with small divisors, e.g. scaling your example by 1e6 gives:

ga-> d 1e6/(1e-8*1e6)
Result value = 1e+08

Unless there's a good reason for the relatively high threshold perhaps we can persuade the developers to use a smaller value in future....?

Doug

-----Original Message-----
From: Semyon Grodsky [mailto:senya at atmos.umd.edu]
Sent: 24 November 2014 18:49
To: GrADS Users Forum
Subject: [gradsusr] grads2.1.a1 bug?

Dear colleagues,
it seems that GRADS2.1.a1 has a bug related to small values, which is illustrated below
ga-> d 1/1e-6
Result value = 1e+06
ga-> d 1/1e-7
Result value = 1e+07
ga-> d 1/1e-8
Result value = -9.99e+08

Any idea what might be causing that?
Thanks,
--Senya
---------------------------------------
ga-> q config
Config: v2.1.a1 little-endian readline grib2 netcdf hdf4-sds hdf5 opendap-grids,stn geotiff shapefile cairo Grid Analysis and Display System (GrADS) Version 2.1.a1 Copyright (c) 1988-2013 by the Institute for Global Environment and Society (IGES) This program is distributed WITHOUT ANY WARRANTY See file COPYRIGHT for more information.

Built Sun Dec 15 10:03:18 EST 2013 for x86_64-unknown-linux-gnu

This version of GrADS has been configured with the following options:
   o Built on a LITTLE ENDIAN machine
   o Athena Widget GUI DISABLED
   o Command line editing ENABLED
       http://tiswww.case.edu/php/chet/readline/rltop.html
   o GRIB2 interface ENABLED
       http://www.ijg.org
       http://www.ece.uvic.ca/~mdadams/jasper
       http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2
       g2clib-1.4.0
   o NetCDF interface ENABLED
       http://www.unidata.ucar.edu/software/netcdf
       netcdf 4.2.1.1 of Nov 15 2013 08:44:30 $
   o OPeNDAP gridded data interface ENABLED
   o OPeNDAP station data interface ENABLED
       http://iges.org/grads/gadoc/supplibs.html
       libgadap 2.0
   o HDF4 and HDF5 interfaces ENABLED
       http://hdfgroup.org
       HDF 4.2r3
       HDF5 1.8.11
   o GeoTIFF and KML/TIFF output ENABLED
       http://www.libtiff.org
       http://geotiff.osgeo.org
   o KML contour output ENABLED
   o Shapefile interface ENABLED
       http://shapelib.maptools.org
   o Cairo graphics interface ENABLED
       http://cairographics.org
       http://cgit.freedesktop.org/pixman
       http://www.freetype.org/index2.html
       http://www.freedesktop.org/wiki/Software/fontconfig
       Cairo 1.12.16
       Pixman 0.28.0
       Freetype 2.4.10
       Fontconfig 2.9.0

For additional information please consult http://iges.org/grads


-----------------------------------------------------------
Semyon Grodsky
Computer and Space Science Building (Bldg. #224), Room 2409 Department of Atmospheric and Oceanic Science University of Maryland College Park, MD 20742

Phone:  301-405-5330
Fax:    301-314-9482
E-mail: senya at atmos.umd.edu
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