chrono::ChSystemDescriptor Class Reference

## Description

Base class for collecting objects inherited from ChConstraint, ChVariables and optionally ChKRMBlock.

These objects can be used to define a sparse representation of the system. This collector is important because it contains all the required information that is sent to a solver (usually a VI/CCP solver, or as a subcase, a linear solver).
The problem is described by a variational inequality VI(Z*x-d,K):
The matrix $$Z$$ that represents the problem has this form:

 | H -Cq'|*|q|- | f|= |0|
| Cq -E | |l|  |-b|  |c|


with $$Y \ni \mathbb{l} \perp \mathbb{c} \in N_y$$
where $$N_y$$ is the normal cone to $$Y$$
By flipping the sign of $$l_i$$, the matrix $$Z$$ can be symmetric (but in general non positive definite)

| H  Cq'|*| q|-| f|=|0|
| Cq  E | |-l| |-b| |c|

• Linear Problem: $$\forall i \,Y_i = \mathbb{R}, N_{y_{i}} = 0$$ (e.g. all bilateral)
• Linear Complementarity Problem (LCP): $$0\le c \perp l\ge0$$ (i.e. $$Y_i = \mathbb{R}^+$$)
• Cone Complementarity Problem (CCP): $$Y \ni \mathbb{l} \perp \mathbb{c} \in N_y$$ ( $$Y_i$$ are friction cones)

Notes

1. most often you call BuildSystemMatrix() right after a dynamic simulation step, in order to get the system matrices updated to the last timestep;
2. when using Anitescu default stepper, the 'f' vector contains forces*timestep = F*dt
3. when using Anitescu default stepper, 'q' represents the 'delta speed',
4. when using Anitescu default stepper, 'b' represents the dt/phi stabilization term.
5. usually, H = M, the mass matrix, but in some cases, ex. when using implicit integrators, objects inherited from ChKRMBlock can be added too, hence H could be H=a*M+b*K+c*R (but not all solvers handle ChKRMBlock!)

All solvers require that the description of the system is passed by means of a ChSystemDescriptor object that holds a list of all the constraints, variables, masses, known terms (ex.forces) under the form of ChVariables, ChConstraints and ChKRMBlock.

In this default implementation, the ChSystemDescriptor simply holds a vector of pointers to ChVariables or to ChConstraints, but more advanced implementations (ex. for supporting parallel GPU solvers) could store constraints and variables structures with other, more efficient data schemes.

#include <ChSystemDescriptor.h>

Inheritance diagram for chrono::ChSystemDescriptor:

## Public Member Functions

std::vector< ChConstraint * > & GetConstraints ()
Access the vector of constraints.

std::vector< ChVariables * > & GetVariables ()
Access the vector of variables.

std::vector< ChKRMBlock * > & GetKRMBlocks ()
Access the vector of KRM matrix blocks.

virtual void BeginInsertion ()
Begin insertion of items.

virtual void InsertConstraint (ChConstraint *mc)
Insert reference to a ChConstraint object.

virtual void InsertVariables (ChVariables *mv)
Insert reference to a ChVariables object.

virtual void InsertKRMBlock (ChKRMBlock *mk)
Insert reference to a ChKRMBlock object (a piece of matrix).

virtual void EndInsertion ()
End insertion of items. More...

virtual unsigned int CountActiveVariables () const
Count & returns the scalar variables in the system. More...

virtual unsigned int CountActiveConstraints () const
Count & returns the scalar constraints in the system This excludes ChConstraint object that are set as inactive. More...

virtual void UpdateCountsAndOffsets ()
Update counts of scalar variables and scalar constraints.

virtual void SetMassFactor (const double mc_a)
Set the c_a coefficient (default=1) used for scaling the M masses of the m_variables. More...

virtual double GetMassFactor ()
Get the c_a coefficient (default=1) used for scaling the M masses of the m_variables.

virtual unsigned int BuildFbVector (ChVectorDynamic<> &Fvector, unsigned int start_row=0) const
Get a vector with all the 'fb' known terms associated to all variables, ordered into a column vector. More...

virtual unsigned int BuildBiVector (ChVectorDynamic<> &Bvector, unsigned int start_row=0) const
Get a vector with all the 'bi' known terms ('constraint residuals') associated to all constraints, ordered into a column vector. More...

virtual unsigned int BuildDiVector (ChVectorDynamic<> &Dvector) const
Get the d vector = {f; -b} with all the 'fb' and 'bi' known terms, as in Z*y-d (it is the concatenation of BuildFbVector and BuildBiVector) The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary. More...

virtual unsigned int BuildDiagonalVector (ChVectorDynamic<> &Diagonal_vect) const
Get the D diagonal of the Z system matrix, as a single column vector (it includes all the diagonal masses of M, and all the diagonal E (-cfm) terms). More...

virtual unsigned int FromVariablesToVector (ChVectorDynamic<> &mvector, bool resize_vector=true) const
Using this function, one may get a vector with all the variables 'q' ordered into a column vector. More...

virtual unsigned int FromVectorToVariables (const ChVectorDynamic<> &mvector)
Using this function, one may go in the opposite direction of the FromVariablesToVector() function, i.e. More...

virtual unsigned int FromConstraintsToVector (ChVectorDynamic<> &mvector, bool resize_vector=true) const
Using this function, one may get a vector with all the constraint reactions 'l_i' ordered into a column vector. More...

virtual unsigned int FromVectorToConstraints (const ChVectorDynamic<> &mvector)
Using this function, one may go in the opposite direction of the FromConstraintsToVector() function, i.e. More...

virtual unsigned int FromUnknownsToVector (ChVectorDynamic<> &mvector, bool resize_vector=true) const
Using this function, one may get a vector with all the unknowns x={q,l} i.e. More...

virtual unsigned int FromVectorToUnknowns (const ChVectorDynamic<> &mvector)
Using this function, one may go in the opposite direction of the FromUnknownsToVector() function, i.e. More...

virtual void SchurComplementProduct (ChVectorDynamic<> &result, const ChVectorDynamic<> &lvector, std::vector< bool > *enabled=nullptr)
Performs the product of N, the Schur complement of the KKT matrix, by an 'l' vector. More...

virtual void SystemProduct (ChVectorDynamic<> &result, const ChVectorDynamic<> &x)
Performs the product of the entire system matrix (KKT matrix), by a vector x ={q,l}. More...

virtual void ConstraintsProject (ChVectorDynamic<> &multipliers)
Performs projection of constraint multipliers onto allowed set (in case of bilateral constraints it does not affect multipliers, but for frictional constraints, for example, it projects multipliers onto the friction cones) Note! the 'l_i' data in the ChConstraints of the system descriptor are changed by this operation (they get the value of 'multipliers' after the projection), so it may happen that you need to backup them via FromConstraintToVector(). More...

virtual void UnknownsProject (ChVectorDynamic<> &mx)
As ConstraintsProject(), but instead of passing the l vector, the entire vector of unknowns x={q,-l} is passed. More...

virtual void ComputeFeasabilityViolation (double &resulting_maxviolation, double &resulting_feasability)
The following (obsolete) function may be called after a solver's 'Solve()' operation has been performed. More...

void PasteMassKRMMatrixInto (ChSparseMatrix &Z, unsigned int start_row=0, unsigned int start_col=0) const
Paste the stiffness, damping or mass matrix of the system into a sparse matrix. More...

unsigned int PasteConstraintsJacobianMatrixInto (ChSparseMatrix &Z, unsigned int start_row=0, unsigned int start_col=0, bool only_bilateral=false) const
Paste the constraints jacobian of the system into a sparse matrix at a given position. More...

unsigned int PasteConstraintsJacobianMatrixTransposedInto (ChSparseMatrix &Z, unsigned int start_row=0, unsigned int start_col=0, bool only_bilateral=false) const
Paste the transposed constraints jacobian of the system into a sparse matrix at a given position. More...

void PasteComplianceMatrixInto (ChSparseMatrix &Z, unsigned int start_row=0, unsigned int start_col=0, bool only_bilateral=false) const
Paste the compliance matrix of the system into a sparse matrix at a given position. More...

virtual void BuildSystemMatrix (ChSparseMatrix *Z, ChVectorDynamic<> *rhs) const
Create and return the assembled system matrix and RHS vector at a given position. More...

virtual void WriteMatrixBlocks (const std::string &path, const std::string &prefix, bool one_indexed=true)
Write the current system matrix blocks and right-hand side components. More...

virtual void WriteMatrix (const std::string &path, const std::string &prefix, bool one_indexed=true)
Write the current assembled system matrix and right-hand side vector. More...

virtual void WriteMatrixSpmv (const std::string &path, const std::string &prefix, bool one_indexed=true)
Write the current assembled system matrix and right-hand side vector. More...

virtual void ArchiveOut (ChArchiveOut &archive_out)
Method to allow serialization of transient data to archives.

virtual void ArchiveIn (ChArchiveIn &archive_in)
Method to allow de-serialization of transient data from archives.

## Protected Attributes

std::vector< ChConstraint * > m_constraints
list of all constraints in the current Chrono system

std::vector< ChVariables * > m_variables
list of all variables in the current Chrono system

std::vector< ChKRMBlock * > m_KRMblocks
list of all KRM blocks in the current Chrono system

double c_a
coefficient form M mass matrices in m_variables

## ◆ BuildBiVector()

 unsigned int chrono::ChSystemDescriptor::BuildBiVector ( ChVectorDynamic<> & Bvector, unsigned int start_row = 0 ) const
virtual

Get a vector with all the 'bi' known terms ('constraint residuals') associated to all constraints, ordered into a column vector.

The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary.

Parameters
 Bvector system-level vector 'b' start_row offset in global 'b' vector

## ◆ BuildDiagonalVector()

 unsigned int chrono::ChSystemDescriptor::BuildDiagonalVector ( ChVectorDynamic<> & Diagonal_vect ) const
virtual

Get the D diagonal of the Z system matrix, as a single column vector (it includes all the diagonal masses of M, and all the diagonal E (-cfm) terms).

The Diagonal_vect must already have the size of n. of unknowns, otherwise it will be resized if necessary).

Parameters
 Diagonal_vect system-level vector of terms on M and E diagonal

## ◆ BuildDiVector()

 unsigned int chrono::ChSystemDescriptor::BuildDiVector ( ChVectorDynamic<> & Dvector ) const
virtual

Get the d vector = {f; -b} with all the 'fb' and 'bi' known terms, as in Z*y-d (it is the concatenation of BuildFbVector and BuildBiVector) The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary.

Parameters
 Dvector system-level vector {f;-b}

## ◆ BuildFbVector()

 unsigned int chrono::ChSystemDescriptor::BuildFbVector ( ChVectorDynamic<> & Fvector, unsigned int start_row = 0 ) const
virtual

Get a vector with all the 'fb' known terms associated to all variables, ordered into a column vector.

The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary.

Parameters
 Fvector system-level vector 'f' start_row offset in global 'f' vector

## ◆ BuildSystemMatrix()

 void chrono::ChSystemDescriptor::BuildSystemMatrix ( ChSparseMatrix * Z, ChVectorDynamic<> * rhs ) const
virtual

Create and return the assembled system matrix and RHS vector at a given position.

Parameters
 [out] Z assembled system matrix [out] rhs assembled RHS vector

## ◆ ComputeFeasabilityViolation()

 void chrono::ChSystemDescriptor::ComputeFeasabilityViolation ( double & resulting_maxviolation, double & resulting_feasability )
virtual

The following (obsolete) function may be called after a solver's 'Solve()' operation has been performed.

This gives an estimate of 'how good' the solver had been in finding the proper solution. Resulting estimates are passed as references in member arguments.

Parameters
 resulting_maxviolation gets the max constraint violation (either bi- and unilateral.) resulting_feasability gets the max feasability as max |l*c| , for unilateral only

## ◆ ConstraintsProject()

 void chrono::ChSystemDescriptor::ConstraintsProject ( ChVectorDynamic<> & multipliers )
virtual

Performs projection of constraint multipliers onto allowed set (in case of bilateral constraints it does not affect multipliers, but for frictional constraints, for example, it projects multipliers onto the friction cones) Note! the 'l_i' data in the ChConstraints of the system descriptor are changed by this operation (they get the value of 'multipliers' after the projection), so it may happen that you need to backup them via FromConstraintToVector().

Parameters
 multipliers system-level vector of 'l_i' multipliers to be projected

## ◆ CountActiveConstraints()

 unsigned int chrono::ChSystemDescriptor::CountActiveConstraints ( ) const
virtual

Count & returns the scalar constraints in the system This excludes ChConstraint object that are set as inactive.

Notes:

• also updates the offsets of all constraints in 'l' global vector (see GetOffset() in ChConstraint).

## ◆ CountActiveVariables()

 unsigned int chrono::ChSystemDescriptor::CountActiveVariables ( ) const
virtual

Count & returns the scalar variables in the system.

This excludes ChVariable object that are set as inactive. Notes:

• the number of scalar variables is not necessarily the number of inserted ChVariable objects, some could be inactive.
• also updates the offsets of all variables in 'q' global vector (see GetOffset() in ChVariables).

## ◆ EndInsertion()

 virtual void chrono::ChSystemDescriptor::EndInsertion ( )
inlinevirtual

End insertion of items.

A derived class should always call UpdateCountsAndOffsets.

## ◆ FromConstraintsToVector()

 unsigned int chrono::ChSystemDescriptor::FromConstraintsToVector ( ChVectorDynamic<> & mvector, bool resize_vector = true ) const
virtual

Using this function, one may get a vector with all the constraint reactions 'l_i' ordered into a column vector.

The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary (but uf you are sure that the vector has already the proper size, you can optimize the performance a bit by setting resize_vector as false). Optionally, you can pass an 'enabled' vector of bools, that must have the same length of the l_i reactions vector; constraints with enabled=false are not handled.

Returns
the number of scalar constr.multipliers (i.e. the rows of the column vector).
Parameters
 mvector system-level vector 'l_i' resize_vector if true, resize vector as necessary

## ◆ FromUnknownsToVector()

 unsigned int chrono::ChSystemDescriptor::FromUnknownsToVector ( ChVectorDynamic<> & mvector, bool resize_vector = true ) const
virtual

Using this function, one may get a vector with all the unknowns x={q,l} i.e.

q variables & l_i constr. ordered into a column vector. The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary (but if you are sure that the vector has already the proper size, you can optimize the performance a bit by setting resize_vector as false).

Returns
the number of scalar unknowns
Parameters
 mvector system-level vector x={q,l} resize_vector if true, resize vector as necessary

## ◆ FromVariablesToVector()

 unsigned int chrono::ChSystemDescriptor::FromVariablesToVector ( ChVectorDynamic<> & mvector, bool resize_vector = true ) const
virtual

Using this function, one may get a vector with all the variables 'q' ordered into a column vector.

The column vector must be passed as a ChMatrix<> object, which will be automatically reset and resized to the proper length if necessary (but if you are sure that the vector has already the proper size, you can optimize the performance a bit by setting resize_vector as false).

Returns
the number of scalar variables (i.e. the rows of the column vector).
Parameters
 mvector system-level vector 'q' resize_vector if true, resize vector as necessary

## ◆ FromVectorToConstraints()

 unsigned int chrono::ChSystemDescriptor::FromVectorToConstraints ( const ChVectorDynamic<> & mvector )
virtual

Using this function, one may go in the opposite direction of the FromConstraintsToVector() function, i.e.

one gives a vector with all the constr.reactions 'l_i' ordered into a column vector, and the constraint objects are updated according to these values. Optionally, you can pass an 'enabled' vector of bools, that must have the same length of the l_i reactions vector; constraints with enabled=false are not handled. NOTE!!! differently from FromConstraintsToVector(), which always works, this function will fail if mvector does not match the amount and ordering of the variable objects!!! (it is up to the user to check this!) btw: most often, this is called after FromConstraintsToVector() to do a kind of 'undo', for example.

Returns
the number of scalar constraint multipliers (i.e. the rows of the column vector).
Parameters
 mvector system-level vector 'l_i'

## ◆ FromVectorToUnknowns()

 unsigned int chrono::ChSystemDescriptor::FromVectorToUnknowns ( const ChVectorDynamic<> & mvector )
virtual

Using this function, one may go in the opposite direction of the FromUnknownsToVector() function, i.e.

one gives a vector with all the unknowns x={q,l} ordered into a column vector, and the variables q and constr.multipliers l objects are updated according to these values. NOTE!!! differently from FromUnknownsToVector(), which always works, this function will fail if mvector does not match the amount and ordering of the variable and constraint objects!!! (it is up to the user to check this!)

Parameters
 mvector system-level vector x={q,l}

## ◆ FromVectorToVariables()

 unsigned int chrono::ChSystemDescriptor::FromVectorToVariables ( const ChVectorDynamic<> & mvector )
virtual

Using this function, one may go in the opposite direction of the FromVariablesToVector() function, i.e.

one gives a vector with all the variables 'q' ordered into a column vector, and the variables objects are updated according to these values. NOTE!!! differently from FromVariablesToVector(), which always works, this function will fail if mvector does not match the amount and ordering of the variable objects!!! (it is up to the user to check this!) btw: most often, this is called after FromVariablesToVector() to do a kind of 'undo', for example.

Returns
the number of scalar variables (i.e. the rows of the column vector).
Parameters
 mvector system-level vector 'q'

## ◆ PasteComplianceMatrixInto()

 void chrono::ChSystemDescriptor::PasteComplianceMatrixInto ( ChSparseMatrix & Z, unsigned int start_row = 0, unsigned int start_col = 0, bool only_bilateral = false ) const

Paste the compliance matrix of the system into a sparse matrix at a given position.

Before calling this function the user needs to:

• resize Z (and potentially call SetZeroValues if the case)
• call LoadKRMMatrices with the desired factors
• call SetMassFactor() with the appropriate value

## ◆ PasteConstraintsJacobianMatrixInto()

 unsigned int chrono::ChSystemDescriptor::PasteConstraintsJacobianMatrixInto ( ChSparseMatrix & Z, unsigned int start_row = 0, unsigned int start_col = 0, bool only_bilateral = false ) const

Paste the constraints jacobian of the system into a sparse matrix at a given position.

Before calling this function the user needs to:

• resize Z (and potentially call SetZeroValues if the case)
• call LoadConstraintJacobians Returns the number of pasted constraints.

## ◆ PasteConstraintsJacobianMatrixTransposedInto()

 unsigned int chrono::ChSystemDescriptor::PasteConstraintsJacobianMatrixTransposedInto ( ChSparseMatrix & Z, unsigned int start_row = 0, unsigned int start_col = 0, bool only_bilateral = false ) const

Paste the transposed constraints jacobian of the system into a sparse matrix at a given position.

Before calling this function the user needs to:

• resize Z (and potentially call SetZeroValues if the case)
• call LoadConstraintJacobians Returns the number of pasted constraints.

## ◆ PasteMassKRMMatrixInto()

 void chrono::ChSystemDescriptor::PasteMassKRMMatrixInto ( ChSparseMatrix & Z, unsigned int start_row = 0, unsigned int start_col = 0 ) const

Paste the stiffness, damping or mass matrix of the system into a sparse matrix.

Before calling this function the user needs to:

• resize Z (and potentially call SetZeroValues if the case)
• call LoadKRMMatrices with the desired factors
• call SetMassFactor() with the appropriate value

## ◆ SchurComplementProduct()

 void chrono::ChSystemDescriptor::SchurComplementProduct ( ChVectorDynamic<> & result, const ChVectorDynamic<> & lvector, std::vector< bool > * enabled = nullptr )
virtual

Performs the product of N, the Schur complement of the KKT matrix, by an 'l' vector.

   result = [N]*l = [ [Cq][M^(-1)][Cq'] - [E] ] * l


where [Cq] are the jacobians, [M] is the mass matrix, [E] is the matrix of the optional cfm 'constraint force mixing' terms for compliant constraints. The N matrix is not built explicitly, to exploit sparsity, it is described by the inserted constraints and inserted variables. Optionally, you can pass an 'enabled' vector of bools, that must have the same length of the l_i reactions vector; constraints with enabled=false are not handled. NOTE! the 'q' data in the ChVariables of the system descriptor is changed by this operation, so it may happen that you need to backup them via FromVariablesToVector() NOTE! currently this function does NOT support the cases that use also ChKRMBlock objects, because it would need to invert the global M+K, that is not diagonal, for doing = [N]*l = [ [Cq][(M+K)^(-1)][Cq'] - [E] ] * l

Parameters
 result result of N * l_i lvector vector to be multiplied enabled optional: vector of "enabled" flags, one per scalar constraint.

## ◆ SetMassFactor()

 virtual void chrono::ChSystemDescriptor::SetMassFactor ( const double mc_a )
inlinevirtual

Set the c_a coefficient (default=1) used for scaling the M masses of the m_variables.

Used when performing SchurComplementProduct(), SystemProduct(), BuildSystemMatrix().

## ◆ SystemProduct()

 void chrono::ChSystemDescriptor::SystemProduct ( ChVectorDynamic<> & result, const ChVectorDynamic<> & x )
virtual

Performs the product of the entire system matrix (KKT matrix), by a vector x ={q,l}.

Note that the 'q' data in the ChVariables of the system descriptor is changed by this operation, so thay may need to be backed up via FromVariablesToVector()

Parameters
 result result vector (multiplication of system matrix by x) x vector to be multiplied

## ◆ UnknownsProject()

 void chrono::ChSystemDescriptor::UnknownsProject ( ChVectorDynamic<> & mx )
virtual

As ConstraintsProject(), but instead of passing the l vector, the entire vector of unknowns x={q,-l} is passed.

Note! the 'l_i' data in the ChConstraints of the system descriptor are changed by this operation (they get the value of 'multipliers' after the projection), so it may happen that you need to backup them via FromConstraintToVector().

Parameters
 mx system-level vector of unknowns x={q,-l} (only the l part is projected)

## ◆ WriteMatrix()

 void chrono::ChSystemDescriptor::WriteMatrix ( const std::string & path, const std::string & prefix, bool one_indexed = true )
virtual

Write the current assembled system matrix and right-hand side vector.

The system matrix is formed by calling BuildSystemMatrix() as used with direct linear solvers. The following files are written in the directory specified by [path]:

• [prefix]_Z.dat the assembled optimization matrix (COO sparse format)
• [prefix]_rhs.dat the assmbled RHS By default, uses 1-based indices (as in Matlab).

## ◆ WriteMatrixBlocks()

 void chrono::ChSystemDescriptor::WriteMatrixBlocks ( const std::string & path, const std::string & prefix, bool one_indexed = true )
virtual

Write the current system matrix blocks and right-hand side components.

The system matrix is formed by calling BuildSystemMatrix() as used with direct linear solvers. The following files are written in the directory specified by [path]:

• [prefix]_H.dat masses and/or stiffness (Matlab sparse format)
• [prefix]_Cq.dat Jacobians (Matlab sparse format)
• [prefix]_E.dat constraint compliance (Matlab sparse format)
• [prefix]_b.dat constraint rhs By default, uses 1-based indices (as in Matlab).

## ◆ WriteMatrixSpmv()

 void chrono::ChSystemDescriptor::WriteMatrixSpmv ( const std::string & path, const std::string & prefix, bool one_indexed = true )
virtual

Write the current assembled system matrix and right-hand side vector.

The system matrix is formed by multiple calls to SystemProduct() as used with iterative linear solvers. The following files are written in the directory specified by [path]:

• [prefix]_Z.dat the assembled optimization matrix (Matlab sparse format)
• [prefix]_rhs.dat the assmbled RHS By default, uses 1-based indices (as in Matlab).

The documentation for this class was generated from the following files:
• /builds/uwsbel/chrono/src/chrono/solver/ChSystemDescriptor.h
• /builds/uwsbel/chrono/src/chrono/solver/ChSystemDescriptor.cpp