[gradsusr] grads2.1.a1 bug?

[Semyon Grodsky]

Doug,
thanks for coming back on that.

I found that replacing 1/1e-8 by pow(1e-8,-1) gives correct result. But, 
I am a bit surprised that developers still keep silence.
Best,
--Senya

On 11/25/2014 4:22 AM, Clark, Douglas B. wrote:
> 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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-- 
-----------------------------------------------------------
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