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tricks - some tricks (and bugs) when using NEMO


One can use cat(1) to catenate structured binary files, e.g.
    cat r001a.dat >>r001.dat

To copy structured binary files between machines of different binary format, use the tsf(1NEMO) , rsf(1NEMO) programs and, if available, the compress(1) , uncompress(1) utilities:

    tsf in=r001.dat maxprec=t allline=t | compress >>
and on the other machine:
    zcat | rsf - r001.dat
On non-Unix supercomputers, often the ASCII "205" format (see e.g. atos(1NEMO) ) will be used. This may be saved in compressed format also, and can be processed by NEMO after
    zcat | atos - r001.dat

Some N-body programs, which are capable of handling a series of snapshots, and selecting them using the times= keyword, are not able to handle subsequent snapshots which are larger than the first one. In fact, unpredictable things may happen, although usually it results in a core because of illegal memory access. There are two solutions. The program can be recompiled, by using a -DREALLOC flag or #define it in the source code. The second solution is to prepend the datafile with a large enough ’dummy’ file.

To display a scatter diagram in the form of a contour map, convert the two columns to a snapshot by calling them ’x’ and ’y’ coordinates. Remaining phase space coordinates are unimportant. Set masses to 1, and use the atos(1NEMO) format. A program like awk(1) can write the file for atos(1NEMO) , then snapgrid(1NEMO) creates a image(5NEMO) file, which can be optionally smoothed using ccdsmooth(1NEMO) and displayed with ccdplot(1NEMO) . In case your host has nicer contour plotting programs, use ccdfits(1NEMO) to write a fits(5NEMO) format file. Check also the tabccd shell script, if available, or perhaps someone wrote it in C already. It calls awk, atos and snapgrid.

The ds(1LOCAL) program, written by Bill Sebok, is one of the external programs which can be used to display images. ds can understand a variety of image file formats, of which the fits(5NEMO) is best suited for our needs. Transform your image to a fits file using ccdfits(1NEMO) , and use ds on that fits file. Although ds(1L) works on monochrome SUN workstations, it’s best on a color monitor. The trick to remember is to use the -yflip switch, or click on the Y button, because our fits interface has a problem obviously...


Peter Teuben.

Update History

18-Aug-88    Document created    PJT 
5-mar-89    tabccd added             PJT
6-mar-89    ds added              PJT
9-oct-90    fixed some typos    PJT

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