Source code for elastica.wrappers.constraints

__doc__ = """
Constraints
-----------

Provides the constraints interface to enforce displacement boundary conditions (see `boundary_conditions.py`).
"""

from elastica.boundary_conditions import FreeRod


[docs]class Constraints: """ The Constraints class is a wrapper for enforcing displacement boundary conditions. To enforce boundary conditions on rod-like objects, the simulator class must be derived from Constraints class. Attributes ---------- _constraints: list List of boundary condition classes defined for rod-like objects. """ def __init__(self): self._constraints = [] super(Constraints, self).__init__()
[docs] def constrain(self, system): """ This method enforces a displacement boundary conditions to the relevant user-defined system or rod-like object. You must input the system or rod-like object that you want to enforce boundary condition on. Parameters ---------- system: object System is a rod-like object. Returns ------- """ sys_idx = self._get_sys_idx_if_valid(system) # Create _Constraint object, cache it and return to user _constraint = _Constraint(sys_idx) self._constraints.append(_constraint) return _constraint
def _finalize(self): # From stored _Constraint objects, instantiate the boundary conditions # inplace : https://stackoverflow.com/a/1208792 # dev : the first index stores the rod index to apply the boundary condition # to. Technically we can use another array but it its one more book-keeping # step. Being lazy, I put them both in the same array self._constraints[:] = [ (constraint.id(), constraint(self._systems[constraint.id()])) for constraint in self._constraints ] # Sort from lowest id to highest id for potentially better memory access # _constraints contains list of tuples. First element of tuple is rod number and # following elements are the type of boundary condition such as # [(0, FreeRod, OneEndFixedRod), (1, HelicalBucklingBC), ... ] # Thus using lambda we iterate over the list of tuples and use rod number (x[0]) # to sort constraints. self._constraints.sort(key=lambda x: x[0]) # At t=0.0, constrain all the boundary conditions (for compatability with # initial conditions) # TODO: you may need to change naming of _callBC self._callBC(time=0.0) # TODO: same as above naming of _callBC function def _callBC(self, time, *args, **kwargs): for sys_id, constraint in self._constraints: constraint.constrain_values(self._systems[sys_id], time, *args, **kwargs) constraint.constrain_rates(self._systems[sys_id], time, *args, **kwargs)
class _Constraint: """ Constraint wrapper private class Attributes ---------- _sys_idx: int _bc_cls: list *args Variable length argument list. **kwargs Arbitrary keyword arguments. """ def __init__(self, sys_idx: int): """ Parameters ---------- sys_idx: int """ self._sys_idx = sys_idx self._bc_cls = None self._args = () self._kwargs = {} def using(self, bc_cls, *args, **kwargs): """ This method is a wrapper to set which boundary condition class is used to enforce boundary condition from user defined rod-like objects. Parameters ---------- bc_cls : object User defined boundary condition class. *args Variable length argument list **kwargs Arbitrary keyword arguments. Returns ------- """ assert issubclass( bc_cls, FreeRod ), "{} is not a valid boundary condition. Did you forget to derive from FreeRod?".format( bc_cls ) self._bc_cls = bc_cls self._args = args self._kwargs = kwargs return self def id(self): return self._sys_idx def __call__(self, rod, *args, **kwargs): """ Constructs a constraint after checks Parameters ---------- args kwargs Returns ------- """ if not self._bc_cls: raise RuntimeError( "No boundary condition provided to constrain rod" "id {0} at {1}, but a BC was intended. Did you" "forget to call the `using` method?".format(self.id(), rod) ) # If there is position, director in kwargs, deal with it first # Returns None if not found pos_indices = self._kwargs.pop( "constrained_position_idx", None ) # calculate position indices as a tuple director_indices = self._kwargs.pop( "constrained_director_idx", None ) # calculate director indices as a tuple # If pos_indices is not None, construct list else empty list # IMPORTANT : do copy for memory-safe operations positions = ( [rod.position_collection[..., idx].copy() for idx in pos_indices] if pos_indices else [] ) directors = ( [rod.director_collection[..., idx].copy() for idx in director_indices] if director_indices else [] ) try: return self._bc_cls(*positions, *directors, *self._args, **self._kwargs) except (TypeError, IndexError): raise TypeError( "Unable to construct boundary condition class. Note that:\n" "1. Any rod properties needed should be placed first\n" "in the boundary_condition __init__ like so (pos_one, pos_two, <other_args>)\n" "2. Number of requested position and directors such as (1, 2) should match\n" "the __init__ method. eg MyBC.__init__(pos_one, director_one, director_two)\n" "should have the `using` call as .using(MyBC, positions=(1,), directors=(1,-1))\n" )