++++ Convex Hull
+chull, the default analysis module, can provide a garantee that there are no
+message inversions after synchronization. When printing the statistics, it
+will print, for each trace, the type of factors found:
+* "Middle", all went according to assumptions and there will be no message
+ inversions
+* "Fallback", it was not possible to garantee no message inversion so
+ approximate factors were given instead. This may happen during long running
+ traces where the non-linearity of the clocks was notable. If you can, try to
+ reduce the duration of the trace. (Sometimes this may happen during a trace
+ as short as 120s. but sometimes traces 30 mins. or longer are ok, your
+ milleage may vary). It would also be to improve the algorithms to avoid
+ this, see the "Todo" section. In any case, you may get better results (but
+ still no garantee) by choosing the linreg algorithm instead.
+* "Absent", the trace pair does not contain common communication events. Are
+ you sure the nodes exchanged TCP traffic during the trace?
+
+There are also other, less common, types. See the enum ApproxType in
+event_analysis_chull.h.
+
++++ Linear Regression
+linreg sometimes gives more accurate results than chull but it provides no
+garantee
+
++++ Synchronization evaluation
+eval is a special module, it doesn't really perform synchronization, instead
+it calculates and prints different metrics about how well traces are
+synchronized. Although it can be run like other analysis modules, it is most
+useful when run in a postprocessing step, after another synchronization module
+has been run. Eval is most common run in text mode. To do this, run:
+lttv -m sync_chain_batch [usual options, ex: -t traces/node1 -t traces/node2
+--sync ...]
+It can also be run from the lttv source tree via runlttv:
+./runlttv -m eval [usual runlttv options, ex: traces/node1 traces/node2]
+
+eval provides a few more options:
+--eval-rtt-file - argument: FILE
+ specify the file containing RTT information
+--eval-graphs - argument: none
+ output gnuplot graph showing synchronization points
+--eval-graphs-dir - argument: eval-graphs-<lttv pid>
+ specify the directory where to store the graphs
+
+The RTT file should contain information on the minimum round-trip time between
+nodes involved in the trace. This information is used (optionally) in the
+evaluation displayed and in the histogram graphs produced. The file should
+contain a series of lines of the form:
+192.168.112.56 192.168.112.57 0.100
+The first two fields are the IP addresses of the source and destination hosts.
+(hostnames are not supported). The last field is the minimum rtt in ms. The
+fields are separated by whitespace. '#' comments a line.
+
+Many commands can be used to measure the RTT, for example:
+ping -s 8 -A -c 8000 -w 10 192.168.112.57
+
+Note that this must be repeated in both directions in the file.
+
+++++ Linear Programming and GLPK
+The synchronization evaluation can optionally perform an analysis similar to
+chull but by using a linear program in one of the steps. This can be used to
+validate a part of the chull algorithm but it can also be used to provide a
+measure of the accuracy of the synchronization in any point (this is seen in
+the graph output).
+
+This is enabled by default at configure time (--with-glpk) if the GNU Linear
+Programming Kit is available (libglpk).
+