Add example of task dependency graph

examples/task_graph/README

+In order to create a task dependency graph, you need to enable the debugging checks
+
+
+=====================================================
+
+ICs extracted from the EAGLE suite of simulations. 
+
+WARNING: These ICs correspond to a very small cosmological volume
+and are not representative of actual load-balancing of large runs.
+
+The particle distribution here is the snapshot 27 (z=0.1) of the 6.25Mpc
+Ref-model. h- and a- factors from the original Gadget code have been
+corrected for. Variables not used in a pure hydro & gravity code have
+been removed. 
+Everything is ready to be run without cosmological integration. 
+
+MD5 checksum of the ICs:
+a4efccd3646a60ad8600ac3a2895ea82  EAGLE_ICs_6.hdf5

examples/task_graph/getIC.sh

+#!/bin/bash
+wget http://virgodb.cosma.dur.ac.uk/swift-webstorage/ICs/EAGLE_ICs_6.hdf5

examples/task_graph/run.sh

+#!/bin/bash
+
+function test {
+    $1
+    if [[ $? -ne 0 ]]; then
+	echo "Swift failed, please verify if you have compiled with debugging checks (--enable-debugging-checks)"
+	exit 1
+    fi
+}
+
+ # Generate the initial conditions if they are not present.
+if [ ! -e EAGLE_ICs_6.hdf5 ]
+then
+    echo "Fetching initial conditions for the EAGLE 6Mpc example..."
+    ./getIC.sh
+fi
+
+test "../swift -x -s task_graph.yml"
+
+dot -Tpng dependency_graph.dot -o task_graph.png
+
+echo "Task dependency graph written in task_graph.png"

examples/task_graph/task_graph.yml

+# Define the system of units to use internally. 
+InternalUnitSystem:
+  UnitMass_in_cgs:     1.989e43      # 10^10 M_sun in grams
+  UnitLength_in_cgs:   3.085678e24   # Mpc in centimeters
+  UnitVelocity_in_cgs: 1e5           # km/s in centimeters per second
+  UnitCurrent_in_cgs:  1             # Amperes
+  UnitTemp_in_cgs:     1             # Kelvin
+
+# Parameters governing the time integration
+TimeIntegration:
+  time_begin: 0.    # The starting time of the simulation (in internal units).
+  time_end:   1e-4  # The end time of the simulation (in internal units).
+  dt_min:     1e-4 # The minimal time-step size of the simulation (in internal units).
+  dt_max:     1e-4  # The maximal time-step size of the simulation (in internal units).
+
+# Parameters governing the snapshots
+Snapshots:
+  basename:            eagle # Common part of the name of output files
+  time_first:          0.    # Time of the first output (in internal units)
+  delta_time:          1e-3  # Time difference between consecutive outputs (in internal units)
+
+# Parameters governing the conserved quantities statistics
+Statistics:
+  delta_time:          1e-2 # Time between statistics output
+
+# Parameters for the self-gravity scheme
+Gravity:
+  eta:                   0.025    # Constant dimensionless multiplier for time integration.
+  theta:                 0.85     # Opening angle (Multipole acceptance criterion)
+  epsilon:               0.001    # Softening length (in internal units).
+  
+# Parameters for the hydrodynamics scheme
+SPH:
+  resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
+
+# Parameters related to the initial conditions
+InitialConditions:
+  file_name:  ./EAGLE_ICs_6.hdf5     # The file to read
+