def to_linearizer(self): """Returns an instance of the Linearizer class, initiated from the data in the KanesMethod class. This may be more desirable than using the linearize class method, as the Linearizer object will allow more efficient recalculation (i.e. about varying operating points).""" if (self._fr is None) or (self._frstar is None): raise ValueError('Need to compute Fr, Fr* first.') # Get required equation components. The Kane's method class breaks # these into pieces. Need to reassemble f_c = self._f_h if self._f_nh and self._k_nh: f_v = self._f_nh + self._k_nh * Matrix(self.u) else: f_v = Matrix() if self._f_dnh and self._k_dnh: f_a = self._f_dnh + self._k_dnh * Matrix(self._udot) else: f_a = Matrix() # Dicts to sub to zero, for splitting up expressions u_zero = dict((i, 0) for i in self.u) ud_zero = dict((i, 0) for i in self._udot) qd_zero = dict((i, 0) for i in self._qdot) qd_u_zero = dict((i, 0) for i in Matrix([self._qdot, self.u])) # Break the kinematic differential eqs apart into f_0 and f_1 f_0 = msubs(self._f_k, u_zero) + self._k_kqdot * Matrix(self._qdot) f_1 = msubs(self._f_k, qd_zero) + self._k_ku * Matrix(self.u) # Break the dynamic differential eqs into f_2 and f_3 f_2 = msubs(self._frstar, qd_u_zero) f_3 = msubs(self._frstar, ud_zero) + self._fr f_4 = zeros(len(f_2), 1) # Get the required vector components q = self.q u = self.u if self._qdep: q_i = q[:-len(self._qdep)] else: q_i = q q_d = self._qdep if self._udep: u_i = u[:-len(self._udep)] else: u_i = u u_d = self._udep # Form dictionary to set auxiliary speeds & their derivatives to 0. uaux = self._uaux uauxdot = uaux.diff(dynamicsymbols._t) uaux_zero = dict((i, 0) for i in Matrix([uaux, uauxdot])) # Checking for dynamic symbols outside the dynamic differential # equations; throws error if there is. sym_list = set(Matrix([q, self._qdot, u, self._udot, uaux, uauxdot])) if any( find_dynamicsymbols(i, sym_list) for i in [ self._k_kqdot, self._k_ku, self._f_k, self._k_dnh, self._f_dnh, self._k_d ]): raise ValueError('Cannot have dynamicsymbols outside dynamic \ forcing vector.') # Find all other dynamic symbols, forming the forcing vector r. # Sort r to make it canonical. r = list(find_dynamicsymbols(msubs(self._f_d, uaux_zero), sym_list)) r.sort(key=default_sort_key) # Check for any derivatives of variables in r that are also found in r. for i in r: if diff(i, dynamicsymbols._t) in r: raise ValueError('Cannot have derivatives of specified \ quantities when linearizing forcing terms.') return Linearizer(f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a, q, u, q_i, q_d, u_i, u_d, r)
def to_linearizer(self, q_ind=None, qd_ind=None, q_dep=None, qd_dep=None): """Returns an instance of the Linearizer class, initiated from the data in the LagrangesMethod class. This may be more desirable than using the linearize class method, as the Linearizer object will allow more efficient recalculation (i.e. about varying operating points). Parameters ========== q_ind, qd_ind : array_like, optional The independent generalized coordinates and speeds. q_dep, qd_dep : array_like, optional The dependent generalized coordinates and speeds. """ # Compose vectors t = dynamicsymbols._t q = self.q u = self._qdots ud = u.diff(t) # Get vector of lagrange multipliers lams = self.lam_vec mat_build = lambda x: Matrix(x) if x else Matrix() q_i = mat_build(q_ind) q_d = mat_build(q_dep) u_i = mat_build(qd_ind) u_d = mat_build(qd_dep) # Compose general form equations f_c = self._hol_coneqs f_v = self.coneqs f_a = f_v.diff(t) f_0 = u f_1 = -u f_2 = self._term1 f_3 = -(self._term2 + self._term4) f_4 = -self._term3 # Check that there are an appropriate number of independent and # dependent coordinates if len(q_d) != len(f_c) or len(u_d) != len(f_v): raise ValueError( ("Must supply {:} dependent coordinates, and " + "{:} dependent speeds").format(len(f_c), len(f_v))) if set(Matrix([q_i, q_d])) != set(q): raise ValueError("Must partition q into q_ind and q_dep, with " + "no extra or missing symbols.") if set(Matrix([u_i, u_d])) != set(u): raise ValueError("Must partition qd into qd_ind and qd_dep, " + "with no extra or missing symbols.") # Find all other dynamic symbols, forming the forcing vector r. # Sort r to make it canonical. insyms = set(Matrix([q, u, ud, lams])) r = list(find_dynamicsymbols(f_3, insyms)) r.sort(key=default_sort_key) # Check for any derivatives of variables in r that are also found in r. for i in r: if diff(i, dynamicsymbols._t) in r: raise ValueError('Cannot have derivatives of specified \ quantities when linearizing forcing terms.') return Linearizer(f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a, q, u, q_i, q_d, u_i, u_d, r, lams)