low level I/O error

[Douglas Clark]

Roop,

It looks as if you are writing 264 values from FORTRAN (i.e.
gpcp_ave(1:264)), but the ctl file has nx=13, ny=11,nt=264, instead of
nx=ny=1.

Some other points:

* form='unformatted' creates a sequential access file by default (I
think - check your file size and if it appears to be 8B larger than
expected you've probably got a sequuential file with start and end of
record values), in which case you need
an "options sequential" record in your ctl file
(see under control file at
http://grads.iges.org/grads/gadoc/gadocindex.html ).
Personally I'd specify access='direct' in the FORTRAN to create a
direct access file, which makes the file structure marginally simpler
and avoids the need for the ctl file "options" stuff. Indeed I have just
seen under the documentation for "options sequential" that
"If your gridded data is written in sequential format, then each record
must be an X-Y varying grid"

whereas you currently write all times to a single record. Looks as if
it would be easier to go for direct access FORTRAN output!

Doug




>>> roop_saini at STUDENT.UML.EDU 02/04/2009 19:58 >>>
Hi,

I am getting the following error beyond t=169:

Low Level I/O Error: Read  error on data file
Data File name = boxave_gpcp.r4
Error reading 13 bytes at location 24180
Data Request Error: Error for variable 'gpcp'
Error occurred at column 1
Display error: Invalid expression
Expression = gpcp

I am using GrADS 1.9.0-rc1 on a PC.

My control file looks like:

dset ^boxave_gpcp.r4
undef -99999.0
title GPCP data
xdef 13 linear 71.25 2.5
ydef 11 linear 6.25 2.5
tdef 264 linear Jan1960 1mo
zdef 01 levels 1
vars 1
gpcp 0 99 monsoon onset GPCP
endvars

I am trying to average "precipitation" over a certain area.

In case, you would like to know what my Fortran program looks like:

       Program Box Average

       parameter(nx=144)
       parameter(ny=72)
       parameter(nt=264)
!       parameter(nlon=13)
!       parameter(nlat=11)
       parameter(lon1=30)
       parameter(lon2=42)
       parameter(lat1=39)
       parameter(lat2=49)
       parameter(undef=-99999.0)

       integer ix
       integer iy
       integer it

       real gpcp(nx,ny,nt)
       real gpcp_ave(nt)
       real count(nt)

       open(13,file="anomaly_gpcp.r4",form="unformatted",
     & recl=nx*ny*nt*4)
       read(13,rec=1)gpcp

       do it=1,nt

             count(it)=0.0
             gpcp_ave(it)=0.0

       enddo

       do ix=lon1,lon2
         do iy=lat1,lat2
           do it=1,nt

             if(gpcp(ix,iy,it).ne.undef) then

             gpcp_ave(it)=gpcp_ave(it)+gpcp(ix,iy,it)
             count(it)=count(it)+1.0

             endif

           enddo
         enddo
       enddo

       do it=1,nt

           gpcp_ave(it)=gpcp_ave(it)/count(it)

       enddo

       open(24,file="boxave_gpcp.r4",form="unformatted",
     &  recl=nt*4)
       write(24,rec=1)gpcp_ave

       write(*,*)"Completed GPCP Box Average"

       stop
       end

Can anyone help me as to what is the problem?

Thanks,
Roop.

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