reinstate the deprecated functions

.gitignore

@@ -3,4 +3,4 @@ dist/
 pylj/__pycache__/
 pylj/tests/__pycache__/
 pylj.egg-info/
-examples/
+pylj/comp.cpython-37m-darwin.so

pylj/pairwise.py

@@ -125,6 +125,55 @@ def second_law(f, m, d1, d2):
     """
     return (f * d1 / d2) / m
 
+def lennard_jones_energy(A, B, dr):
+    """pairwise.lennard_jones_energy has been deprecated, please use
+    forcefields.lennard_jones instead
+
+    Calculate the energy of a pair of particles at a given distance.
+
+    Parameters
+    ----------
+    A: float
+        The value of the A parameter for the Lennard-Jones potential.
+    B: float
+        The value of the B parameter for the Lennard-Jones potential.
+    dr: float
+        The distance between the two particles.
+
+    Returns
+    -------
+    float:
+        The potential energy between the two particles.
+    """
+    print("pairwise.lennard_jones_energy has been deprecated, please use "
+          "forcefields.lennard_jones instead")
+    return A * np.power(dr, -12) - B * np.power(dr, -6)
+
+
+def lennard_jones_force(A, B, dr):
+    """pairwise.lennard_jones_energy has been deprecated, please use
+    forcefields.lennard_jones with force=True instead
+
+    Calculate the force between a pair of particles at a given distance.
+
+    Parameters
+    ----------
+    A: float
+        The value of the A parameter for the Lennard-Jones potential.
+    B: float
+        The value of the B parameter for the Lennard-Jones potential.
+    dr: float
+        The distance between the two particles.
+
+    Returns
+    -------
+    float:
+        The force between the two particles.
+    """
+    print("pairwise.lennard_jones_energy has been deprecated, please use "
+          "forcefields.lennard_jones with force=True instead")
+    return 12 * A * np.power(dr, -13) - 6 * B * np.power(dr, -7)
+
 
 def compute_energy(particles, box_length, cut_off, constants, forcefield):
     r"""Calculates the total energy of the simulation.