Running make in this directory will generate a number of PDF graphs.
In the callgraph, the arrows means "calls".  In the dependency graphs,
the arrows means "requires" (or "depends upon").

callgraph.pdf             This shows the callgraph, i.e., what functions each
                          function in the program calls.
module_dependencies.pdf   This shows the dependencies between the modules.
file_dependencies.pdf     This shows the dependencies between the files.
makefile_dependencies.pdf This shows the dependencies required by make when
                          building the program.
build_dependencies.pdf    This is like makefile_dependencies.pdf but shows
                          the operations performed to generate the new file.

callgraph.d               This shows the callgraph in text format.
files.d                   This shows the file dependencies in text format.
modules.d                 This shows the module dependencies in text format.