/usr/include/dune/localfunctions/lagrange/qk/qklocalbasis.hh is in libdune-localfunctions-dev 2.4.1-1.
This file is owned by root:root, with mode 0o644.
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// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_LOCALFUNCTIONS_QKLOCALBASIS_HH
#define DUNE_LOCALFUNCTIONS_QKLOCALBASIS_HH
#include <dune/common/fvector.hh>
#include <dune/common/fmatrix.hh>
#include <dune/common/power.hh>
#include <dune/geometry/type.hh>
#include <dune/localfunctions/common/localbasis.hh>
#include <dune/localfunctions/common/localfiniteelementtraits.hh>
namespace Dune
{
/**@ingroup LocalBasisImplementation
\brief Lagrange shape functions of order k on the reference cube.
Also known as \f$Q^k\f$.
\tparam D Type to represent the field in the domain.
\tparam R Type to represent the field in the range.
\tparam k Polynomial degree
\tparam d Dimension of the cube
\nosubgrouping
*/
template<class D, class R, int k, int d>
class QkLocalBasis
{
enum { n = StaticPower<k+1,d>::power };
// ith Lagrange polynomial of degree k in one dimension
static R p (int i, D x)
{
R result(1.0);
for (int j=0; j<=k; j++)
if (j!=i) result *= (k*x-j)/(i-j);
return result;
}
// derivative of ith Lagrange polynomial of degree k in one dimension
static R dp (int i, D x)
{
R result(0.0);
for (int j=0; j<=k; j++)
if (j!=i)
{
R prod( (k*1.0)/(i-j) );
for (int l=0; l<=k; l++)
if (l!=i && l!=j)
prod *= (k*x-l)/(i-l);
result += prod;
}
return result;
}
// Return i as a d-digit number in the (k+1)-nary system
static Dune::FieldVector<int,d> multiindex (int i)
{
Dune::FieldVector<int,d> alpha;
for (int j=0; j<d; j++)
{
alpha[j] = i % (k+1);
i = i/(k+1);
}
return alpha;
}
public:
typedef LocalBasisTraits<D,d,Dune::FieldVector<D,d>,R,1,Dune::FieldVector<R,1>,Dune::FieldMatrix<R,1,d>, 1> Traits;
//! \brief number of shape functions
unsigned int size () const
{
return StaticPower<k+1,d>::power;
}
//! \brief Evaluate all shape functions
inline void evaluateFunction (const typename Traits::DomainType& in,
std::vector<typename Traits::RangeType>& out) const
{
out.resize(size());
for (size_t i=0; i<size(); i++)
{
// convert index i to multiindex
Dune::FieldVector<int,d> alpha(multiindex(i));
// initialize product
out[i] = 1.0;
// dimension by dimension
for (int j=0; j<d; j++)
out[i] *= p(alpha[j],in[j]);
}
}
/** \brief Evaluate Jacobian of all shape functions
* \param in position where to evaluate
* \param out The return value
*/
inline void
evaluateJacobian (const typename Traits::DomainType& in,
std::vector<typename Traits::JacobianType>& out) const
{
out.resize(size());
// Loop over all shape functions
for (size_t i=0; i<size(); i++)
{
// convert index i to multiindex
Dune::FieldVector<int,d> alpha(multiindex(i));
// Loop over all coordinate directions
for (int j=0; j<d; j++)
{
// Initialize: the overall expression is a product
// if j-th bit of i is set to -1, else 1
out[i][0][j] = dp(alpha[j],in[j]);
// rest of the product
for (int l=0; l<d; l++)
if (l!=j)
out[i][0][j] *= p(alpha[l],in[l]);
}
}
}
/** \brief Evaluate derivative in a given direction
* \param [in] direction The direction to derive in
* \param [in] in Position where to evaluate
* \param [out] out The return value
*/
template<int diffOrder>
inline void evaluate(
const std::array<int,1>& direction,
const typename Traits::DomainType& in,
std::vector<typename Traits::RangeType>& out) const
{
static_assert(diffOrder == 1, "We only can compute first derivatives");
out.resize(size());
// Loop over all shape functions
for (size_t i=0; i<size(); i++)
{
// convert index i to multiindex
Dune::FieldVector<int,d> alpha(multiindex(i));
// Loop over all coordinate directions
std::size_t j = direction[0];
// Initialize: the overall expression is a product
// if j-th bit of i is set to -1, else 1
out[i][0] = dp(alpha[j],in[j]);
// rest of the product
for (std::size_t l=0; l<d; l++)
if (l!=j)
out[i][0] *= p(alpha[l],in[l]);
}
}
//! \brief Polynomial order of the shape functions
unsigned int order () const
{
return k;
}
};
}
#endif
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