Dihedral class

topology/__init__.py

@@ -6,8 +6,11 @@
 from .core.connection import Connection
 from .core.bond import Bond
 from .core.angle import Angle
+from .core.dihedral import Dihedral
+
 
 from .core.potential import Potential
 from .core.atom_type import AtomType
 from .core.bond_type import BondType
 from .core.angle_type import AngleType
+from .core.dihedral_type import DihedralType

topology/core/dihedral.py

@@ -0,0 +1,65 @@
+import warnings
+
+from topology.core.connection import Connection
+from topology.core.dihedral_type import DihedralType
+from topology.exceptions import TopologyError
+
+
+class Dihedral(Connection):
+    """A 4-partner connection between sites.
+
+    Partners
+    --------
+    connection_members: list of topology.Site
+        Should be length 4
+    connection_type : topology.DihedralType
+    name : name of the dihedral
+        inherits the name attribute from Connection
+
+    Notes
+    -----
+    Inherits some methods from Connection:
+        __eq__, __repr__, _validate methods
+    Addiitonal _validate methods are presented
+    """
+
+    def __init__(self, connection_members=[], connection_type=None, name="Dihedral"):
+        connection_members = _validate_four_partners(connection_members)
+        connection_type = _validate_dihedraltype(connection_type)
+
+        super(Dihedral, self).__init__(connection_members=connection_members,
+                connection_type=connection_type, name=name)
+
+    def __eq__(self, other):
+        return hash(self) == hash(other)
+
+    def __hash__(self):
+        if self.connection_type:
+            return hash(
+                tuple(
+                    (
+                        self.name,
+                        self.connection_type,
+                        tuple(self.connection_members),
+                    )
+                )
+            )
+        return hash(tuple(self.connection_members))
+
+
+def _validate_four_partners(connection_members):
+    """Ensure 4 partners are involved in Dihedral"""
+    if len(connection_members) != 4:
+        raise TopologyError("Trying to create an Dihedral "
+                "with {} connection members". format(len(connection_members)))
+
+    return connection_members
+
+
+def _validate_dihedraltype(contype):
+    """Ensure connection_type is a DihedralType """
+    if contype is None:
+        warnings.warn("Non-parametrized Dihedral detected")
+    elif not isinstance(contype, DihedralType):
+        raise TopologyError("Supplied non-DihedralType {}".format(contype))
+    return contype

topology/core/dihedral_type.py

@@ -0,0 +1,67 @@
+import warnings
+import unyt as u
+
+from topology.core.potential import Potential
+from topology.exceptions import TopologyError
+
+
+class DihedralType(Potential):
+    """A Potential between 4-bonded partners.
+
+    Parameters
+    ----------
+    name : str
+    expression : str or sympy.Expression
+        See `Potential` documentation for more information
+    parameters : dict {str, unyt.unyt_quantity}
+        See `Potential` documentation for more information
+    independent vars : set of str
+        See `Potential` documentation for more information
+    member_types : list of topology.AtomType.name (str)
+
+    Notes
+    ----
+    Inherits many functions from topology.Potential:
+        __eq__, _validate functions
+    """
+
+    def __init__(self,
+                 name='DihedralType',
+                 expression='k * (1 + cos(n * phi - phi_eq))**2',
+                 parameters={
+                     'k': 1000 * u.Unit('kJ / (deg**2)'),
+                     'phi_eq': 180 * u.deg,
+                     'n': 1*u.dimensionless
+                 },
+                 independent_variables={'phi'},
+                 member_types=[]):
+
+        super(DihedralType, self).__init__(name=name, expression=expression,
+                parameters=parameters, independent_variables=independent_variables)
+
+        self._member_types = _validate_four_member_type_names(member_types)
+
+    @property
+    def member_types(self):
+        return self._member_types
+
+    @member_types.setter
+    def member_types(self, val):
+        if self.member_types != val:
+            warnings.warn("Changing an DihedralType's constituent "
+                    "member types: {} to {}".format(self.member_types, val))
+        self._member_types = _validate_four_member_type_names(val)
+
+    def __repr__(self):
+        return "<DihedralType {}, id {}>".format(self.name, id(self))
+
+def _validate_four_member_type_names(types):
+    """Ensure 4 partners are involved in DihedralType"""
+    if len(types) != 4 and len(types) != 0:
+        raise TopologyError("Trying to create an DihedralType "
+                "with {} constituent types". format(len(types)))
+    if not all([isinstance(t, str) for t in types]):
+        raise TopologyError("Types passed to DihedralType "
+                            "need to be strings corresponding to AtomType names")
+
+    return types

topology/core/topology.py

@@ -6,9 +6,11 @@
 
 from topology.core.bond import Bond
 from topology.core.angle import Angle
+from topology.core.dihedral import Dihedral
 from topology.core.potential import Potential
 from topology.core.bond_type import BondType
 from topology.core.angle_type import AngleType
+from topology.core.dihedral_type import DihedralType
 from topology.exceptions import TopologyError
 
 
@@ -25,18 +27,18 @@ def __init__(self, name="Topology", box=None):
             self._name = name
         self._box = box
         self._sites = IndexedSet()
+        self._typed = False
         self._connections = IndexedSet()
         self._bonds = IndexedSet()
         self._angles = IndexedSet()
-
+        self._dihedrals = IndexedSet()
         self._subtops = IndexedSet()
-
         self._typed = False
         self._atom_types = IndexedSet()
         self._connection_types = IndexedSet()
         self._bond_types = IndexedSet()
         self._angle_types = IndexedSet()
-
+        self._dihedral_types = IndexedSet()
         self._combining_rule = 'lorentz'
 
     @property
@@ -118,6 +120,9 @@ def add_connection(self, connection, update_types=True):
             self.update_bonds()
         elif isinstance(connection, Angle):
             self.update_angles()
+        elif isinstance(connection, Dihedral):
+            self.update_dihedrals()
+
         self.update_connections()
 
         if update_types:
@@ -127,6 +132,8 @@ def add_connection(self, connection, update_types=True):
                 self.update_bond_types()
             elif isinstance(connection, Angle):
                 self.update_angle_types()
+            elif isinstance(connection, Dihedral):
+                self.update_dihedral_types()
             self.update_connection_types()
 
     def add_subtopology(self, subtop):
@@ -151,6 +158,10 @@ def n_bonds(self):
     def n_angles(self):
         return len(self.angles)
 
+    @property
+    def n_dihedrals(self):
+        return len(self.dihedrals)
+
     @property
     def subtops(self):
         return self._subtops
@@ -175,6 +186,10 @@ def bonds(self):
     def angles(self):
         return self._angles
 
+    @property
+    def dihedrals(self):
+        return self._dihedrals
+
     @property
     def atom_types(self):
         return self._atom_types
@@ -191,6 +206,10 @@ def bond_types(self):
     def angle_types(self):
         return self._angle_types
 
+    @property
+    def dihedral_types(self):
+        return self._dihedral_types
+
     @property
     def atom_type_expressions(self):
         return list(set([atype.expression for atype in self.atom_types]))
@@ -207,24 +226,30 @@ def bond_type_expressions(self):
     def angle_type_expressions(self):
         return list(set([atype.expression for atype in self.angle_types]))
 
+    @property
+    def dihedral_type_expressions(self):
+        return list(set([atype.expression for atype in self.dihedral_types]))
+
     def update_top(self, update_types=True):
         """ Update the entire topology's attributes
 
         Notes
         -----
-        Will update: sites, connections, bonds, angles,
-        atom_types, connectiontypes, bondtypes, angletypes
+        Will update: sites, connections, bonds, angles, dihedrals
+        atom_types, connectiontypes, bondtypes, angletypes, dihedral_types
         """
         self.update_sites()
         self.update_connections()
         self.update_bonds()
         self.update_angles()
+        self.update_dihedrals()
 
         if update_types:
             self.update_atom_types()
             self.update_connection_types()
             self.update_bond_types()
             self.update_angle_types()
+            self.update_dihedral_types()
             self.is_typed()
 
     def update_sites(self):
@@ -251,6 +276,10 @@ def update_angles(self):
         """ Rebuild the angle list by filtering through connection list """
         self._angles = [a for a in self.connections if isinstance(a, Angle)]
 
+    def update_dihedrals(self):
+        """ Rebuild the dihedral list by filtering through connection list """
+        self._dihedrals = [d for d in self.connections if isinstance(d, Dihedral)]
+
     def update_atom_types(self):
         """ Update the atom types based on the site list """
         #self._atom_types = []
@@ -296,6 +325,18 @@ def update_angle_types(self):
             elif a.connection_type not in self.angle_types:
                 self.angle_types.add(a.connection_type)
 
+    def update_dihedral_types(self):
+        """ Update the dihedral types based on the dihedral list """
+        #self._dihedral_types = []
+        for d in self.dihedrals:
+            if d.connection_type is None:
+                warnings.warn("Non-parametrized Dihedral {} detected".format(d))
+            elif not isinstance(d.connection_type, DihedralType):
+                raise TopologyError("Non-DihedralType {} found in Dihedral {}".format(
+                    d.connection_type, d))
+            elif d.connection_type not in self.dihedral_types:
+                self.dihedral_types.add(d.connection_type)
+
     def __repr__(self):
         descr = list('<')
         descr.append(self.name + ' ')

topology/tests/test_angle.py

@@ -44,7 +44,7 @@ def test_angle_parametrized(self):
         assert site3.n_connections == 1
         assert len(connect.connection_members) == 3
         assert connect.connection_type is not None
-        assert connect.name == "angle_name"
+        assert connect.name == 'angle_name'
 
     def test_angle_fake(self):
         site1 = Site(name='site1')
@@ -67,7 +67,7 @@ def test_angle_constituent_types(self):
         site3 = Site(name='site3', position=[1,1,0], atom_type=AtomType(name='C'))
         angtype = AngleType(member_types=[site1.atom_type.name, site2.atom_type.name,
             site3.atom_type.name])
-        ang = Angle(connection_members=[site1, site2,site3], 
+        ang = Angle(connection_members=[site1, site2, site3], 
                 connection_type=angtype)
         assert 'A' in ang.connection_type.member_types
         assert 'B' in ang.connection_type.member_types

topology/tests/test_bond.py

@@ -38,7 +38,7 @@ def test_bond_parametrized(self):
         assert site2.n_connections == 1
         assert len(connect.connection_members) == 2
         assert connect.connection_type is not None
-        assert connect.name == "bond_name"
+        assert connect.name == 'bond_name'
 
     def test_bond_fake(self):
         site1 = Site(name='site1')