gridfunc.hpp

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// Copyright (c) 2010, Lawrence Livermore National Security, LLC. Produced at
// the Lawrence Livermore National Laboratory. LLNL-CODE-443211. All Rights
// reserved. See file COPYRIGHT for details.
//
// This file is part of the MFEM library. For more information and source code
// availability see http://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the GNU Lesser General Public License (as published by the Free
// Software Foundation) version 2.1 dated February 1999.

#ifndef MFEM_GRIDFUNC
#define MFEM_GRIDFUNC

#include "../config/config.hpp"
#include "fespace.hpp"
#include "coefficient.hpp"
#include "bilininteg.hpp"
#include <limits>
#include <ostream>
#include <string>

namespace mfem
{

/// Class for grid function - Vector with associated FE space.
class GridFunction : public Vector
{
protected:
   /// FE space on which grid function lives.
   FiniteElementSpace *fes;

   /// Used when the grid function is read from a file
   FiniteElementCollection *fec;

   long sequence; // see FiniteElementSpace::sequence, Mesh::sequence

   /** Optional, internal true-dof vector: if the FiniteElementSpace #fes has a
       non-trivial (i.e. not NULL) prolongation operator, this Vector may hold
       associated true-dof values - either owned or external. */
   Vector t_vec;

   void SaveSTLTri(std::ostream &out, double p1[], double p2[], double p3[]);

   void GetVectorGradientHat(ElementTransformation &T, DenseMatrix &gh) const;

   // Project the delta coefficient without scaling and return the (local)
   // integral of the projection.
   void ProjectDeltaCoefficient(DeltaCoefficient &delta_coeff,
                                double &integral);

   // Sum fluxes to vertices and count element contributions
   void SumFluxAndCount(BilinearFormIntegrator &blfi,
                        GridFunction &flux,
                        Array<int>& counts,
                        int wcoef,
                        int subdomain);

   /** Project a discontinuous vector coefficient in a continuous space and
       return in dof_attr the maximal attribute of the elements containing each
       degree of freedom. */
   void ProjectDiscCoefficient(VectorCoefficient &coeff, Array<int> &dof_attr);

   void Destroy();

public:

   GridFunction() { fes = NULL; fec = NULL; sequence = 0; }

   /// Copy constructor.
   GridFunction(const GridFunction &orig)
      : Vector(orig), fes(orig.fes), fec(NULL), sequence(orig.sequence) { }

   /// Construct a GridFunction associated with the FiniteElementSpace @a *f.
   GridFunction(FiniteElementSpace *f) : Vector(f->GetVSize())
   { fes = f; fec = NULL; sequence = f->GetSequence(); }

   /// Construct a GridFunction using previously allocated array @a data.
   /** The GridFunction does not assume ownership of @a data which is assumed to
       be of size at least `f->GetVSize()`. Similar to the Vector constructor
       for externally allocated array, the pointer @a data can be NULL. The data
       array can be replaced later using the method SetData().
    */
   GridFunction(FiniteElementSpace *f, double *data) : Vector(data, f->GetVSize())
   { fes = f; fec = NULL; sequence = f->GetSequence(); }

   /// Construct a GridFunction on the given Mesh, using the data from @a input.
   /** The content of @a input should be in the format created by the method
       Save(). The reconstructed FiniteElementSpace and FiniteElementCollection
       are owned by the GridFunction. */
   GridFunction(Mesh *m, std::istream &input);

   GridFunction(Mesh *m, GridFunction *gf_array[], int num_pieces);

   /// Make the GridFunction the owner of 'fec' and 'fes'
   void MakeOwner(FiniteElementCollection *_fec) { fec = _fec; }

   FiniteElementCollection *OwnFEC() { return fec; }

   int VectorDim() const;

   /// Read only access to the (optional) internal true-dof Vector.
   /** Note that the returned Vector may be empty, if not previously allocated
       or set. */
   const Vector &GetTrueVector() const { return t_vec; }
   /// Read and write access to the (optional) internal true-dof Vector.
   /** Note that the returned Vector may be empty, if not previously allocated
       or set. */
   Vector &GetTrueVector() { return t_vec; }

   /// @brief Extract the true-dofs from the GridFunction. If all dofs are true,
   /// then `tv` will be set to point to the data of `*this`.
   void GetTrueDofs(Vector &tv) const;

   /// Shortcut for calling GetTrueDofs() with GetTrueVector() as argument.
   void SetTrueVector() { GetTrueDofs(GetTrueVector()); }

   /// Set the GridFunction from the given true-dof vector.
   virtual void SetFromTrueDofs(const Vector &tv);

   /// Shortcut for calling SetFromTrueDofs() with GetTrueVector() as argument.
   void SetFromTrueVector() { SetFromTrueDofs(GetTrueVector()); }

   /// Returns the values in the vertices of i'th element for dimension vdim.
   void GetNodalValues(int i, Array<double> &nval, int vdim = 1) const;

   virtual double GetValue(int i, const IntegrationPoint &ip,
                           int vdim = 1) const;

   void GetVectorValue(int i, const IntegrationPoint &ip, Vector &val) const;

   void GetValues(int i, const IntegrationRule &ir, Vector &vals,
                  int vdim = 1) const;

   void GetValues(int i, const IntegrationRule &ir, Vector &vals,
                  DenseMatrix &tr, int vdim = 1) const;

   int GetFaceValues(int i, int side, const IntegrationRule &ir, Vector &vals,
                     DenseMatrix &tr, int vdim = 1) const;

   void GetVectorValues(ElementTransformation &T, const IntegrationRule &ir,
                        DenseMatrix &vals) const;

   void GetVectorValues(int i, const IntegrationRule &ir,
                        DenseMatrix &vals, DenseMatrix &tr) const;

   int GetFaceVectorValues(int i, int side, const IntegrationRule &ir,
                           DenseMatrix &vals, DenseMatrix &tr) const;

   void GetValuesFrom(const GridFunction &orig_func);

   void GetBdrValuesFrom(const GridFunction &orig_func);

   void GetVectorFieldValues(int i, const IntegrationRule &ir,
                             DenseMatrix &vals,
                             DenseMatrix &tr, int comp = 0) const;

   /// For a vector grid function, makes sure that the ordering is byNODES.
   void ReorderByNodes();

   /// Return the values as a vector on mesh vertices for dimension vdim.
   void GetNodalValues(Vector &nval, int vdim = 1) const;

   void GetVectorFieldNodalValues(Vector &val, int comp) const;

   void ProjectVectorFieldOn(GridFunction &vec_field, int comp = 0);

   void GetDerivative(int comp, int der_comp, GridFunction &der);

   double GetDivergence(ElementTransformation &tr) const;

   void GetCurl(ElementTransformation &tr, Vector &curl) const;

   void GetGradient(ElementTransformation &tr, Vector &grad) const;

   void GetGradients(const int elem, const IntegrationRule &ir,
                     DenseMatrix &grad) const;

   void GetVectorGradient(ElementTransformation &tr, DenseMatrix &grad) const;

   /** Compute \f$ (\int_{\Omega} (*this) \psi_i)/(\int_{\Omega} \psi_i) \f$,
       where \f$ \psi_i \f$ are the basis functions for the FE space of avgs.
       Both FE spaces should be scalar and on the same mesh. */
   void GetElementAverages(GridFunction &avgs) const;

   /** Impose the given bounds on the function's DOFs while preserving its local
    *  integral (described in terms of the given weights) on the i'th element
    *  through SLBPQ optimization.
    *  Intended to be used for discontinuous FE functions. */
   void ImposeBounds(int i, const Vector &weights,
                     const Vector &_lo, const Vector &_hi);
   void ImposeBounds(int i, const Vector &weights,
                     double _min = 0.0, double _max = infinity());

   /** @brief Project the @a src GridFunction to @a this GridFunction, both of
       which must be on the same mesh. */
   /** The current implementation assumes that all elements use the same
       projection matrix. */
   void ProjectGridFunction(const GridFunction &src);

   virtual void ProjectCoefficient(Coefficient &coeff);

   // call fes -> BuildDofToArrays() before using this projection
   void ProjectCoefficient(Coefficient &coeff, Array<int> &dofs, int vd = 0);

   void ProjectCoefficient(VectorCoefficient &vcoeff);

   // call fes -> BuildDofToArrays() before using this projection
   void ProjectCoefficient(VectorCoefficient &vcoeff, Array<int> &dofs);

   void ProjectCoefficient(Coefficient *coeff[]);

   /** @brief Project a discontinuous vector coefficient as a grid function on
       a continuous finite element space. The values in shared dofs are
       determined from the element with maximal attribute. */
   virtual void ProjectDiscCoefficient(VectorCoefficient &coeff);

   enum AvgType {ARITHMETIC, HARMONIC};
   /** @brief Projects a discontinuous coefficient so that the values in shared
       vdofs are computed by taking an average of the possible values. */
   virtual void ProjectDiscCoefficient(Coefficient &coeff, AvgType type);
   /** @brief Projects a discontinuous _vector_ coefficient so that the values
       in shared vdofs are computed by taking an average of the possible values.
   */
   virtual void ProjectDiscCoefficient(VectorCoefficient &coeff, AvgType type);

protected:
   /** @brief Accumulates (depending on @a type) the values of @a coeff at all
       shared vdofs and counts in how many zones each vdof appears. */
   void AccumulateAndCountZones(Coefficient &coeff, AvgType type,
                                Array<int> &zones_per_vdof);

   /** @brief Accumulates (depending on @a type) the values of @a vcoeff at all
       shared vdofs and counts in how many zones each vdof appears. */
   void AccumulateAndCountZones(VectorCoefficient &vcoeff, AvgType type,
                                Array<int> &zones_per_vdof);

   // Complete the computation of averages; called e.g. after
   // AccumulateAndCountZones().
   void ComputeMeans(AvgType type, Array<int> &zones_per_vdof);

public:
   void ProjectBdrCoefficient(Coefficient &coeff, Array<int> &attr)
   {
      Coefficient *coeff_p = &coeff;
      ProjectBdrCoefficient(&coeff_p, attr);
   }

   void ProjectBdrCoefficient(Coefficient *coeff[], Array<int> &attr);

   /** Project the normal component of the given VectorCoefficient on
       the boundary. Only boundary attributes that are marked in
       'bdr_attr' are projected. Assumes RT-type VectorFE GridFunction. */
   void ProjectBdrCoefficientNormal(VectorCoefficient &vcoeff,
                                    Array<int> &bdr_attr);

   /** Project the tangential components of the given VectorCoefficient on
       the boundary. Only boundary attributes that are marked in
       'bdr_attr' are projected. Assumes ND-type VectorFE GridFunction. */
   void ProjectBdrCoefficientTangent(VectorCoefficient &vcoeff,
                                     Array<int> &bdr_attr);

   virtual double ComputeL2Error(Coefficient &exsol,
                                 const IntegrationRule *irs[] = NULL) const
   { return ComputeLpError(2.0, exsol, NULL, irs); }

   virtual double ComputeL2Error(Coefficient *exsol[],
                                 const IntegrationRule *irs[] = NULL) const;

   virtual double ComputeL2Error(VectorCoefficient &exsol,
                                 const IntegrationRule *irs[] = NULL,
                                 Array<int> *elems = NULL) const;

   virtual double ComputeH1Error(Coefficient *exsol, VectorCoefficient *exgrad,
                                 Coefficient *ell_coef, double Nu,
                                 int norm_type) const;

   virtual double ComputeMaxError(Coefficient &exsol,
                                  const IntegrationRule *irs[] = NULL) const
   {
      return ComputeLpError(infinity(), exsol, NULL, irs);
   }

   virtual double ComputeMaxError(Coefficient *exsol[],
                                  const IntegrationRule *irs[] = NULL) const;

   virtual double ComputeMaxError(VectorCoefficient &exsol,
                                  const IntegrationRule *irs[] = NULL) const
   {
      return ComputeLpError(infinity(), exsol, NULL, NULL, irs);
   }

   virtual double ComputeL1Error(Coefficient &exsol,
                                 const IntegrationRule *irs[] = NULL) const
   { return ComputeLpError(1.0, exsol, NULL, irs); }

   virtual double ComputeW11Error(Coefficient *exsol, VectorCoefficient *exgrad,
                                  int norm_type, Array<int> *elems = NULL,
                                  const IntegrationRule *irs[] = NULL) const;

   virtual double ComputeL1Error(VectorCoefficient &exsol,
                                 const IntegrationRule *irs[] = NULL) const
   { return ComputeLpError(1.0, exsol, NULL, NULL, irs); }

   virtual double ComputeLpError(const double p, Coefficient &exsol,
                                 Coefficient *weight = NULL,
                                 const IntegrationRule *irs[] = NULL) const;

   /** When given a vector weight, compute the pointwise (scalar) error as the
       dot product of the vector error with the vector weight. Otherwise, the
       scalar error is the l_2 norm of the vector error. */
   virtual double ComputeLpError(const double p, VectorCoefficient &exsol,
                                 Coefficient *weight = NULL,
                                 VectorCoefficient *v_weight = NULL,
                                 const IntegrationRule *irs[] = NULL) const;

   virtual void ComputeFlux(BilinearFormIntegrator &blfi,
                            GridFunction &flux,
                            int wcoef = 1, int subdomain = -1);

   /// Redefine '=' for GridFunction = constant.
   GridFunction &operator=(double value);

   /// Copy the data from @a v.
   /** The size of @a v must be equal to the size of the FiniteElementSpace
       @a fes. */
   GridFunction &operator=(const Vector &v);

   /// Copy the data from @a v.
   /** The GridFunctions @a v and @a *this must have FiniteElementSpaces with
       the same size. */
   GridFunction &operator=(const GridFunction &v);

   /// Transform by the Space UpdateMatrix (e.g., on Mesh change).
   virtual void Update();

   FiniteElementSpace *FESpace() { return fes; }
   const FiniteElementSpace *FESpace() const { return fes; }

   /// Associate a new FiniteElementSpace with the GridFunction.
   /** The GridFunction is resized using the SetSize() method. */
   virtual void SetSpace(FiniteElementSpace *f);

   /** @brief Make the GridFunction reference external data on a new
       FiniteElementSpace. */
   /** This method changes the FiniteElementSpace associated with the
       GridFunction and sets the pointer @a v as external data in the
       GridFunction. */
   virtual void MakeRef(FiniteElementSpace *f, double *v);

   /** @brief Make the GridFunction reference external data on a new
       FiniteElementSpace. */
   /** This method changes the FiniteElementSpace associated with the
       GridFunction and sets the data of the Vector @a v (plus the @a v_offset)
       as external data in the GridFunction.
       @note This version of the method will also perform bounds checks when
       the build option MFEM_DEBUG is enabled. */
   virtual void MakeRef(FiniteElementSpace *f, Vector &v, int v_offset);

   /** @brief Associate a new FiniteElementSpace and new true-dof data with the
       GridFunction. */
   /** - If the prolongation matrix of @a f is trivial (i.e. its method
         FiniteElementSpace::GetProlongationMatrix() returns NULL), then the
         method MakeRef() is called with the same arguments.
       - Otherwise, the method SetSpace() is called with argument @a f.
       - The internal true-dof vector is set to reference @a tv. */
   void MakeTRef(FiniteElementSpace *f, double *tv);

   /** @brief Associate a new FiniteElementSpace and new true-dof data with the
       GridFunction. */
   /** - If the prolongation matrix of @a f is trivial (i.e. its method
         FiniteElementSpace::GetProlongationMatrix() returns NULL), this method
         calls MakeRef() with the same arguments.
       - Otherwise, this method calls SetSpace() with argument @a f.
       - The internal true-dof vector is set to reference the sub-vector of
         @a tv starting at the offset @a tv_offset. */
   void MakeTRef(FiniteElementSpace *f, Vector &tv, int tv_offset);

   /// Save the GridFunction to an output stream.
   virtual void Save(std::ostream &out) const;

   /** Write the GridFunction in VTK format. Note that Mesh::PrintVTK must be
       called first. The parameter ref > 0 must match the one used in
       Mesh::PrintVTK. */
   void SaveVTK(std::ostream &out, const std::string &field_name, int ref);

   void SaveSTL(std::ostream &out, int TimesToRefine = 1);

   /// Destroys grid function.
   virtual ~GridFunction() { Destroy(); }
};


/** Overload operator<< for std::ostream and GridFunction; valid also for the
    derived class ParGridFunction */
std::ostream &operator<<(std::ostream &out, const GridFunction &sol);


/** @brief Class representing a function through its values (scalar or vector)
    at quadrature points. */
class QuadratureFunction : public Vector
{
protected:
   QuadratureSpace *qspace; ///< Associated QuadratureSpace
   int vdim;                ///< Vector dimension
   bool own_qspace;         ///< QuadratureSpace ownership flag

public:
   /// Create an empty QuadratureFunction.
   /** The object can be initialized later using the SetSpace() methods. */
   QuadratureFunction()
      : qspace(NULL), vdim(0), own_qspace(false) { }

   /// Create a QuadratureFunction based on the given QuadratureSpace.
   /** The QuadratureFunction does not assume ownership of the QuadratureSpace.
       @note The Vector data is not initialized. */
   QuadratureFunction(QuadratureSpace *qspace_, int vdim_ = 1)
      : Vector(vdim_*qspace_->GetSize()),
        qspace(qspace_), vdim(vdim_), own_qspace(false) { }

   /** @brief Create a QuadratureFunction based on the given QuadratureSpace,
       using the external data, @a qf_data. */
   /** The QuadratureFunction does not assume ownership of neither the
       QuadratureSpace nor the external data. */
   QuadratureFunction(QuadratureSpace *qspace_, double *qf_data, int vdim_ = 1)
      : Vector(qf_data, vdim_*qspace_->GetSize()),
        qspace(qspace_), vdim(vdim_), own_qspace(false) { }

   /// Read a QuadratureFunction from the stream @a in.
   /** The QuadratureFunction assumes ownership of the read QuadratureSpace. */
   QuadratureFunction(Mesh *mesh, std::istream &in);

   virtual ~QuadratureFunction() { if (own_qspace) { delete qspace; } }

   /// Get the associated QuadratureSpace.
   QuadratureSpace *GetSpace() const { return qspace; }

   /// Change the QuadratureSpace and optionally the vector dimension.
   /** If the new QuadratureSpace is different from the current one, the
       QuadratureFunction will not assume ownership of the new space; otherwise,
       the ownership flag remains the same.

       If the new vector dimension @a vdim_ < 0, the vector dimension remains
       the same.

       The data size is updated by calling Vector::SetSize(). */
   inline void SetSpace(QuadratureSpace *qspace_, int vdim_ = -1);

   /** @brief Change the QuadratureSpace, the data array, and optionally the
       vector dimension. */
   /** If the new QuadratureSpace is different from the current one, the
       QuadratureFunction will not assume ownership of the new space; otherwise,
       the ownership flag remains the same.

       If the new vector dimension @a vdim_ < 0, the vector dimension remains
       the same.

       The data array is replaced by calling Vector::NewDataAndSize(). */
   inline void SetSpace(QuadratureSpace *qspace_, double *qf_data,
                        int vdim_ = -1);

   /// Get the vector dimension.
   int GetVDim() const { return vdim; }

   /// Set the vector dimension, updating the size by calling Vector::SetSize().
   void SetVDim(int vdim_)
   { vdim = vdim_; SetSize(vdim*qspace->GetSize()); }

   /// Get the QuadratureSpace ownership flag.
   bool OwnsSpace() { return own_qspace; }

   /// Set the QuadratureSpace ownership flag.
   void SetOwnsSpace(bool own) { own_qspace = own; }

   /// Redefine '=' for QuadratureFunction = constant.
   QuadratureFunction &operator=(double value);

   /// Copy the data from @a v.
   /** The size of @a v must be equal to the size of the QuadratureSpace
       @a qspace. */
   QuadratureFunction &operator=(const Vector &v);

   /// Copy the data from @a v.
   /** The QuadratureFunctions @a v and @a *this must have QuadratureSpaces with
       the same size. */
   QuadratureFunction &operator=(const QuadratureFunction &v);

   /// Get the IntegrationRule associated with mesh element @a idx.
   const IntegrationRule &GetElementIntRule(int idx) const
   { return qspace->GetElementIntRule(idx); }

   /// Return all values associated with mesh element @a idx in a Vector.
   /** The result is stored in the Vector @a values as a reference to the
       global values.

       Inside the Vector @a values, the index `i+vdim*j` corresponds to the
       `i`-th vector component at the `j`-th quadrature point.
    */
   inline void GetElementValues(int idx, Vector &values);

   /// Return all values associated with mesh element @a idx in a Vector.
   /** The result is stored in the Vector @a values as a copy of the
       global values.

       Inside the Vector @a values, the index `i+vdim*j` corresponds to the
       `i`-th vector component at the `j`-th quadrature point.
    */
   inline void GetElementValues(int idx, Vector &values) const;

   /// Return all values associated with mesh element @a idx in a DenseMatrix.
   /** The result is stored in the DenseMatrix @a values as a reference to the
       global values.

       Inside the DenseMatrix @a values, the `(i,j)` entry corresponds to the
       `i`-th vector component at the `j`-th quadrature point.
    */
   inline void GetElementValues(int idx, DenseMatrix &values);

   /// Return all values associated with mesh element @a idx in a const DenseMatrix.
   /** The result is stored in the DenseMatrix @a values as a copy of the
       global values.

       Inside the DenseMatrix @a values, the `(i,j)` entry corresponds to the
       `i`-th vector component at the `j`-th quadrature point.
    */
   inline void GetElementValues(int idx, DenseMatrix &values) const;

   /// Write the QuadratureFunction to the stream @a out.
   void Save(std::ostream &out) const;
};

/// Overload operator<< for std::ostream and QuadratureFunction.
std::ostream &operator<<(std::ostream &out, const QuadratureFunction &qf);


double ZZErrorEstimator(BilinearFormIntegrator &blfi,
                        GridFunction &u,
                        GridFunction &flux,
                        Vector &error_estimates,
                        Array<int> *aniso_flags = NULL,
                        int with_subdomains = 1);

/// Compute the Lp distance between two grid functions on the given element.
double ComputeElementLpDistance(double p, int i,
                                GridFunction& gf1, GridFunction& gf2);


/// Class used for extruding scalar GridFunctions
class ExtrudeCoefficient : public Coefficient
{
private:
   int n;
   Mesh *mesh_in;
   Coefficient &sol_in;
public:
   ExtrudeCoefficient(Mesh *m, Coefficient &s, int _n)
      : n(_n), mesh_in(m), sol_in(s) { }
   virtual double Eval(ElementTransformation &T, const IntegrationPoint &ip);
   virtual ~ExtrudeCoefficient() { }
};

/// Extrude a scalar 1D GridFunction, after extruding the mesh with Extrude1D.
GridFunction *Extrude1DGridFunction(Mesh *mesh, Mesh *mesh2d,
                                    GridFunction *sol, const int ny);


// Inline methods

inline void QuadratureFunction::SetSpace(QuadratureSpace *qspace_, int vdim_)
{
   if (qspace_ != qspace)
   {
      if (own_qspace) { delete qspace; }
      qspace = qspace_;
      own_qspace = false;
   }
   vdim = (vdim_ < 0) ? vdim : vdim_;
   SetSize(vdim*qspace->GetSize());
}

inline void QuadratureFunction::SetSpace(QuadratureSpace *qspace_,
                                         double *qf_data, int vdim_)
{
   if (qspace_ != qspace)
   {
      if (own_qspace) { delete qspace; }
      qspace = qspace_;
      own_qspace = false;
   }
   vdim = (vdim_ < 0) ? vdim : vdim_;
   NewDataAndSize(qf_data, vdim*qspace->GetSize());
}

inline void QuadratureFunction::GetElementValues(int idx, Vector &values)
{
   const int s_offset = qspace->element_offsets[idx];
   const int sl_size = qspace->element_offsets[idx+1] - s_offset;
   values.NewDataAndSize(data + vdim*s_offset, vdim*sl_size);
}

inline void QuadratureFunction::GetElementValues(int idx, Vector &values) const
{
   const int s_offset = qspace->element_offsets[idx];
   const int sl_size = qspace->element_offsets[idx+1] - s_offset;
   values.SetSize(vdim*sl_size);
   double *q = data + vdim*s_offset;
   for (int i = 0; i<values.Size(); i++)
   {
      values(i) = *(q++);
   }
}

inline void QuadratureFunction::GetElementValues(int idx, DenseMatrix &values)
{
   const int s_offset = qspace->element_offsets[idx];
   const int sl_size = qspace->element_offsets[idx+1] - s_offset;
   values.Reset(data + vdim*s_offset, vdim, sl_size);
}

inline void QuadratureFunction::GetElementValues(int idx,
                                                 DenseMatrix &values) const
{
   const int s_offset = qspace->element_offsets[idx];
   const int sl_size = qspace->element_offsets[idx+1] - s_offset;
   values.SetSize(vdim, sl_size);
   double *q = data + vdim*s_offset;
   for (int j = 0; j<sl_size; j++)
      for (int i = 0; i<vdim; i++)
      {
         values(i,j) = *(q++);
      }
}

} // namespace mfem

#endif