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20020405: Surface decoder DMSFC is not working

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  • Subject: 20020405: Surface decoder DMSFC is not working
  • Date: Sat, 06 Apr 2002 10:23:58 -0700
>From: Eirh-Yu Hsie <address@hidden>
>Organization: Aeronomy Laboratory/NOAA/DOC
>Keywords: 200204052006.g35K6ca26173 McIDAS-XCD DMSFC

Hsie,

>The surfece decoder DMSFC in my new server (rainbow.al.noaa.gov, RedHat
>Linux 7.2 system) is not working properly.  It fires up and dies
>immediately.  I need your help to take a look at it.

I logged onto rainbow yesterday afternoon and examined where dmsfc.k
was failing.  As a side comment, and mainly for the email archives,
you do this by:

<login as 'mcidas'>
cd workdata                  <- linux/workdata in your case
mcenv                        <- start a mini-McIDAS session
ucu.k POKE 142 0             <- allows McIDAS routines to produce core files
dmsfc.k                      <- failed and dumped core
exit                         <- exit the mini-McIDAS session

cd ~/mcidas7.8/src
gdb dmsfc.k ~/workdata/core  <- ~/linux/workdata/core in your case

This won't tell one much unless dmsfc.k was compiled with the debug
flag, -g, set (DEBUG=-g in makefile) and stripping turned off
(STRIP=  in makefile).  Once I did this, I found that the routine
was getting a floating point exception in a 'mod' call:

"m0dcdsfc.for" line 4259:

         speed  = float(mod(value,spdmod))
         dir    = value / spdmod

It seems that spdmod was zero, and mod was failing.  Since this doesn't
seem to happen with code built with gcc/f2c, I have to wonder about
the code generated with g77.  Even if the mod routine didn't dump core, the
next line would cause a floating point exception (divide by zero).

I modified the code to:

         if ( spdmod .ne. 0 ) then          ! <<<<< UPC mod 20030405 >>>>>
           speed  = float(mod(value,spdmod))
           dir    = value / spdmod
         else
           goto 100
         endif

and rebuilt and reinstalled dmsfc.k.  Since it started running correctly
immediately after doing this, I am satisfied that the fix was the right
approach.

(Again, most of these comments are designed for the inquiry tracking system.)

Tom