How to compare reco and L3 data

1. Run reco on the raw data file of your choice and keep the raw data chunk (see here).
2. On the outputfile (the DST file, usually called outputfile_XX by default) of 1) run TrigSim.
3. D0reco and Trigsim do not have to be from the same release version. (But as always, the release you are using for reco has to be frozen, otherwise your file will become unusable once this happens. You have been warned.)
4. When running Trigsim, you can comment out the bit that writes out thumbnails. You won't need them.
5. Make a working directory somewhere and do 'addpkg analysis_example'. I am currently using p15.06.01.
6. In this package Marco Verzocchi has written a nice example program on how to access different chunks and write the results to histograms or an ntuple. Go look at it.
7. Do a 'gmake all' to make an executable.
8. Run it, either using rund0exe ('setup d0tools') or directly, by editing analysis_example/rcp/ReadEvent.rcp and using runD0ChunkAnalyze_DST.rcp as the framwork executable.
9. Look at the results.
10. Here is a bit of example code on how to access Level 3 information. Note that 'online' refers to chunks written during data taking, while 'offline' refers to trigsim output. You need to define which chunk you want. If you don't the program will compile and run, but I don't know which chunk you get either !