Class LagrangianLinearTIDS

Defined in Program listing for file kernel/src/modelingTools/LagrangianLinearTIDS.hpp

class LagrangianLinearTIDS : public LagrangianDS

Lagrangian Linear Systems with time invariant coefficients - \(M\dot v + Cv + Kq = F_{ext}(t,z) + p \).

The class LagrangianLinearTIDS allows to define and compute a generic ndof-dimensional Lagrangian Linear Time Invariant Dynamical System of the form :

\( M \ddot q + C \dot q + K q = F_{ext}(t,z) + p, \)

where

  • \(q \in R^{ndof} \) is the set of the generalized coordinates,

  • \( \dot q \in R^{ndof} \) the velocity, i. e. the time derivative of the generalized coordinates.

  • \( \ddot q \in R^{ndof} \) the acceleration, i. e. the second time derivative of the generalized coordinates.

  • \( p \in R^{ndof} \) the forces due to the Non Smooth Interaction. In particular case of Non Smooth evolution, the variable p contains the impulse and not the force.

  • \( M \in R^{ndof \times ndof} \) is the Mass matrix (access : mass() method).

  • \( K \in R^{ndof \times ndof} \) is the stiffness matrix (access : K() method).

  • \( C \in R^{ndof \times ndof} \) is the viscosity matrix (access : C() method).

  • \( z \in R^{zSize}\) is a vector of arbitrary algebraic variables, some sort of discret state.

The equation of motion is also shortly denoted as: \( M(q,z) \dot v = F(v, q, t, z) + p \)

where

  • \(F(v, q, t, z) \in R^{ndof} \) collects the total forces acting on the system, that is \( F(v, q, t, z) = F_{ext}(t, z) - Cv - Kq \).

This vector is saved and may be accessed using forces() method.

If required (e.g. for Event-Driven like simulation), reformulation as a first-order system is also available, and writes:

  • \( n= 2 ndof \)

  • \( x = \left[\begin{array}{c}q \\ \dot q\end{array}\right]\)

  • rhs given by:

\[\begin{split}rhs(x,t,z) = \left[\begin{array}{c} \dot q \\ \ddot q = M^{-1}\left[F_{ext}(t, z) - C \dot q - K q + p \right]\\ \end{array}\right]\end{split}\]
Its jacobian is:

\[\begin{split}\nabla_{x}rhs(x,t) = \left[\begin{array}{cc} 0 & I \\ -M^{-1}K & -M^{-1}C \\ \end{array}\right]\end{split}\]

with the input due to the non smooth law:

\[\begin{split}r = \left[\begin{array}{c}0 \\ p \end{array}\right]\end{split}\]

public constructors

LagrangianLinearTIDS(SP::SiconosVector q0, SP::SiconosVector v0, SP::SiconosMatrix M, SP::SiconosMatrix K, SP::SiconosMatrix C)

constructor from initial state and all matrix operators.

Parameters
  • q0: initial coordinates

  • v0: initial velocity

  • M: mass matrix

  • K: stiffness matrix

  • C: damping matrix

LagrangianLinearTIDS(SP::SiconosVector q0, SP::SiconosVector v0, SP::SiconosMatrix M)

constructor from initial state and mass matrix only.

Leads to \( M\dot v = F_{ext}(t,z) + p\).

Parameters
  • q0: initial coordinates

  • v0: initial velocity

  • M: mass matrix

~LagrangianLinearTIDS()

destructor

Right-hand side computation

void initRhs(double t)

allocate (if needed) and compute rhs and its jacobian.

Parameters
  • t: time of initialization

void computeForces(double time, SP::SiconosVector q, SP::SiconosVector velocity)

Compute \(F(v,q,t,z)\).

Parameters
  • time: the current time

  • q: SP::SiconosVector: pointers on q

  • velocity: SP::SiconosVector: pointers on velocity

Attributes access

const SimpleMatrix getK() const

get a copy of the stiffness matrix

Return

SimpleMatrix

SP::SiconosMatrix K() const

get stiffness matrix (pointer link)

Return

pointer on a SiconosMatrix

void setK(const SiconosMatrix &K)

set (copy) the value of the stiffness matrix

Parameters
  • K: new stiffness matrix

void setKPtr(SP::SiconosMatrix newPtr)

set stiffness matrix (pointer link)

Parameters
  • newPtr: pointer to the new Stiffness matrix

const SimpleMatrix getC() const

get a copy of the damping matrix

Return

SimpleMatrix

SP::SiconosMatrix C() const

get damping matrix (pointer link)

Return

pointer on a SiconosMatrix

void setC(const SiconosMatrix &C)

set (copy) the value of the damping matrix

Parameters
  • C: new damping matrix

void setCPtr(SP::SiconosMatrix newPtr)

set damping matrix (pointer link)

Parameters
  • newPtr: pointer to the new damping matrix

SP::SiconosMatrix jacobianqForces() const

get \( \nabla_qF(v,q,t,z)\) (pointer link)

Return

pointer on a SiconosMatrix

SP::SiconosMatrix jacobianvForces() const

get \( \nabla_{\dot q}F(v,q,t,z)\) (pointer link)

Return

pointer on a SiconosMatrix

Miscellaneous public methods

virtual bool isLinear()

Return

true if the Dynamical system is linear.

void display(bool brief = true) const

print the data onto the screen