downsample.doc

Instructions for downsampling highres data.

Example Input file:  Ia00000.0000.[uvh]   512^2 data file.

First compile the "convert" code:

% ./gridsetup.py 1 1 1 512 512 1 

edit dns/src/convert.F90 and set the variables "tstart" and "tstop" to 0.0000
which tells the code we to convert the data files from time 0000.0000

Then look for this block of code, around line 108:
  if (convert_opt==0) then  ! -cout uvw     
     call input_uvw(time,Q,vor,work1,work2,1)  ! default headers
  endif
And make sure we are using the "default headers" input_uvw() subroutine call.
Sometimes I change this to read headerless input files, and you will
have to change it back if you do a "cvs update"


% make convert
% ./convert -b -cout uvw -so -smax 128 -d /ccs/wingate/period/Ia0  Ia0  < sh2.inp

-b:  byteswap the input file
-cout uvw:    reoutput u,v and h
-so           output spectral coefficients (instead of default grid point data)
-smax         output spectral coefficients suitable for a 128^2 grid
-d path       directory for data files
Ia0           run name


This will create  .us, .vs and .hs data files which contain spectral
coefficients.  Now we want to convert these to grid point values.
First rename the spectral files (otherwise, when we convert back
to grid point data, it will overright the original data files)

Rename the files to:  Ia0-128-0000.0000.[uvh]s

Recompile convert with a lower resolution:
./gridsetup.py 1 1 1 128 128 1 
make convert

% ./convert -cout uvw -si -d /ccs/wingate/period/Ia0  Ia0-128-  < sh2.inp

-cout uvw:    reoutput u,v and h
-si           input spectral coefficients (instead of default grid point data)
-d path       directory for data files
Ia0           run name



===============================================================================


Another example:   512^3 -> 256^2

# spectral output uvw:
./gridsetup.py 1 1 16 512 512 512
make convert
mpirun -np 16  ./convert  -so -smax 256 -cout uvw -i test.inp -b -d /home/scratch/taylorm/dns iso12_512

# read spectral in, output vorm:
./gridsetup.py 1 1 16 256  256  256 
make convert
mpirun -np 16  ./convert  -si -cout vorm -i test.inp \
    -d /home/scratch/taylorm/dns iso12_512-new.