ElemUtil.cpp

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#include <iostream>
#include <limits>
#include <cassert>

#include "ElemUtil.hpp"
#include "moab/BoundBox.hpp"

namespace moab
{
namespace ElemUtil
{

    bool debug = false;

    /**\brief Class representing a 3-D mapping function (e.g. shape function for volume element) */
    class VolMap
    {
      public:
        /**\brief Return \f$\vec \xi\f$ corresponding to logical center of element */
        virtual CartVect center_xi() const = 0;
        /**\brief Evaluate mapping function (calculate \f$\vec x = F($\vec \xi)\f$ )*/
        virtual CartVect evaluate( const CartVect& xi ) const = 0;
        /**\brief Evaluate Jacobian of mapping function */
        virtual Matrix3 jacobian( const CartVect& xi ) const = 0;
        /**\brief Evaluate inverse of mapping function (calculate \f$\vec \xi = F^-1($\vec x)\f$ )*/
        bool solve_inverse( const CartVect& x, CartVect& xi, double tol ) const;
    };

    bool VolMap::solve_inverse( const CartVect& x, CartVect& xi, double tol ) const
    {
        const double error_tol_sqr = tol * tol;
        double det;
        xi             = center_xi();
        CartVect delta = evaluate( xi ) - x;
        Matrix3 J;
        while( delta % delta > error_tol_sqr )
        {
            J   = jacobian( xi );
            det = J.determinant();
            if( det < std::numeric_limits< double >::epsilon() ) return false;
            xi -= J.inverse() * delta;
            delta = evaluate( xi ) - x;
        }
        return true;
    }

    /**\brief Shape function for trilinear hexahedron */
    class LinearHexMap : public VolMap
    {
      public:
        LinearHexMap( const CartVect* corner_coords ) : corners( corner_coords ) {}
        virtual CartVect center_xi() const;
        virtual CartVect evaluate( const CartVect& xi ) const;
        virtual double evaluate_scalar_field( const CartVect& xi, const double* f_vals ) const;
        virtual Matrix3 jacobian( const CartVect& xi ) const;

      private:
        const CartVect* corners;
        static const double corner_xi[8][3];
    };

    const double LinearHexMap::corner_xi[8][3] = { { -1, -1, -1 }, { 1, -1, -1 }, { 1, 1, -1 }, { -1, 1, -1 },
                                                   { -1, -1, 1 },  { 1, -1, 1 },  { 1, 1, 1 },  { -1, 1, 1 } };
    CartVect LinearHexMap::center_xi() const
    {
        return CartVect( 0.0 );
    }

    CartVect LinearHexMap::evaluate( const CartVect& xi ) const
    {
        CartVect x( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double N_i =
                ( 1 + xi[0] * corner_xi[i][0] ) * ( 1 + xi[1] * corner_xi[i][1] ) * ( 1 + xi[2] * corner_xi[i][2] );
            x += N_i * corners[i];
        }
        x *= 0.125;
        return x;
    }

    double LinearHexMap::evaluate_scalar_field( const CartVect& xi, const double* f_vals ) const
    {
        double f( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double N_i =
                ( 1 + xi[0] * corner_xi[i][0] ) * ( 1 + xi[1] * corner_xi[i][1] ) * ( 1 + xi[2] * corner_xi[i][2] );
            f += N_i * f_vals[i];
        }
        f *= 0.125;
        return f;
    }

    Matrix3 LinearHexMap::jacobian( const CartVect& xi ) const
    {
        Matrix3 J( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double xi_p      = 1 + xi[0] * corner_xi[i][0];
            const double eta_p     = 1 + xi[1] * corner_xi[i][1];
            const double zeta_p    = 1 + xi[2] * corner_xi[i][2];
            const double dNi_dxi   = corner_xi[i][0] * eta_p * zeta_p;
            const double dNi_deta  = corner_xi[i][1] * xi_p * zeta_p;
            const double dNi_dzeta = corner_xi[i][2] * xi_p * eta_p;
            J( 0, 0 ) += dNi_dxi * corners[i][0];
            J( 1, 0 ) += dNi_dxi * corners[i][1];
            J( 2, 0 ) += dNi_dxi * corners[i][2];
            J( 0, 1 ) += dNi_deta * corners[i][0];
            J( 1, 1 ) += dNi_deta * corners[i][1];
            J( 2, 1 ) += dNi_deta * corners[i][2];
            J( 0, 2 ) += dNi_dzeta * corners[i][0];
            J( 1, 2 ) += dNi_dzeta * corners[i][1];
            J( 2, 2 ) += dNi_dzeta * corners[i][2];
        }
        return J *= 0.125;
    }

    bool nat_coords_trilinear_hex( const CartVect* corner_coords, const CartVect& x, CartVect& xi, double tol )
    {
        return LinearHexMap( corner_coords ).solve_inverse( x, xi, tol );
    }
    //
    // nat_coords_trilinear_hex2
    //  Duplicate functionality of nat_coords_trilinear_hex using hex_findpt
    //
    void nat_coords_trilinear_hex2( const CartVect hex[8], const CartVect& xyz, CartVect& ncoords, double etol )

    {
        const int ndim            = 3;
        const int nverts          = 8;
        const int vertMap[nverts] = { 0, 1, 3, 2, 4, 5, 7, 6 };  // Map from nat to lex ordering

        const int n = 2;                 // linear
        realType coords[ndim * nverts];  // buffer

        realType* xm[ndim];
        for( int i = 0; i < ndim; i++ )
            xm[i] = coords + i * nverts;

        // stuff hex into coords
        for( int i = 0; i < nverts; i++ )
        {
            realType vcoord[ndim];
            hex[i].get( vcoord );

            for( int d = 0; d < ndim; d++ )
                coords[d * nverts + vertMap[i]] = vcoord[d];
        }

        double dist = 0.0;
        ElemUtil::hex_findpt( xm, n, xyz, ncoords, dist );
        if( 3 * MOAB_POLY_EPS < dist )
        {
            // outside element, set extremal values to something outside range
            for( int j = 0; j < 3; j++ )
            {
                if( ncoords[j] < ( -1.0 - etol ) || ncoords[j] > ( 1.0 + etol ) ) ncoords[j] *= 10;
            }
        }
    }
    bool point_in_trilinear_hex( const CartVect* hex, const CartVect& xyz, double etol )
    {
        CartVect xi;
        return nat_coords_trilinear_hex( hex, xyz, xi, etol ) && ( fabs( xi[0] - 1.0 ) < etol ) &&
               ( fabs( xi[1] - 1.0 ) < etol ) && ( fabs( xi[2] - 1.0 ) < etol );
    }

    bool point_in_trilinear_hex( const CartVect* hex,
                                 const CartVect& xyz,
                                 const CartVect& box_min,
                                 const CartVect& box_max,
                                 double etol )
    {
        // all values scaled by 2 (eliminates 3 flops)
        const CartVect mid = box_max + box_min;
        const CartVect dim = box_max - box_min;
        const CartVect pt  = 2 * xyz - mid;
        return ( fabs( pt[0] - dim[0] ) < etol ) && ( fabs( pt[1] - dim[1] ) < etol ) &&
               ( fabs( pt[2] - dim[2] ) < etol ) && point_in_trilinear_hex( hex, xyz, etol );
    }

    // Wrapper to James Lottes' findpt routines
    // hex_findpt
    // Find the parametric coordinates of an xyz point inside
    // a 3d hex spectral element with n nodes per dimension
    // xm: coordinates fields, value of x,y,z for each of then n*n*n gauss-lobatto nodes. Nodes are
    // in lexicographical order (x is fastest-changing) n: number of nodes per dimension -- n=2 for
    // a linear element xyz: input, point to find rst: output: parametric coords of xyz inside the
    // element. If xyz is outside the element, rst will be the coords of the closest point dist:
    // output: distance between xyz and the point with parametric coords rst
    /*extern "C"{
    #include "types.h"
    #include "poly.h"
    #include "tensor.h"
    #include "findpt.h"
    #include "extrafindpt.h"
    #include "errmem.h"
    }*/

    void hex_findpt( realType* xm[3], int n, CartVect xyz, CartVect& rst, double& dist )
    {

        // compute stuff that only depends on the order -- could be cached
        realType* z[3];
        lagrange_data ld[3];
        opt_data_3 data;

        // triplicates
        for( int d = 0; d < 3; d++ )
        {
            z[d] = tmalloc( realType, n );
            lobatto_nodes( z[d], n );
            lagrange_setup( &ld[d], z[d], n );
        }

        opt_alloc_3( &data, ld );

        // find nearest point
        realType x_star[3];
        xyz.get( x_star );

        realType r[3] = { 0, 0, 0 };  // initial guess for parametric coords
        unsigned c    = opt_no_constraints_3;
        dist          = opt_findpt_3( &data, (const realType**)xm, x_star, r, &c );
        // c tells us if we landed inside the element or exactly on a face, edge, or node

        // copy parametric coords back
        rst = r;

        // Clean-up (move to destructor if we decide to cache)
        opt_free_3( &data );
        for( int d = 0; d < 3; ++d )
            lagrange_free( &ld[d] );
        for( int d = 0; d < 3; ++d )
            free( z[d] );
    }

    // hex_eval
    // Evaluate a field in a 3d hex spectral element with n nodes per dimension, at some given
    // parametric coordinates field: field values for each of then n*n*n gauss-lobatto nodes. Nodes
    // are in lexicographical order (x is fastest-changing) n: number of nodes per dimension -- n=2
    // for a linear element rst: input: parametric coords of the point where we want to evaluate the
    // field value: output: value of field at rst

    void hex_eval( realType* field, int n, CartVect rstCartVec, double& value )
    {
        int d;
        realType rst[3];
        rstCartVec.get( rst );

        // can cache stuff below
        lagrange_data ld[3];
        realType* z[3];
        for( d = 0; d < 3; ++d )
        {
            z[d] = tmalloc( realType, n );
            lobatto_nodes( z[d], n );
            lagrange_setup( &ld[d], z[d], n );
        }

        // cut and paste -- see findpt.c
        const unsigned nf = n * n, ne = n, nw = 2 * n * n + 3 * n;
        realType* od_work = tmalloc( realType, 6 * nf + 9 * ne + nw );

        // piece that we shouldn't want to cache
        for( d = 0; d < 3; d++ )
        {
            lagrange_0( &ld[d], rst[d] );
        }

        value = tensor_i3( ld[0].J, ld[0].n, ld[1].J, ld[1].n, ld[2].J, ld[2].n, field, od_work );

        // all this could be cached
        for( d = 0; d < 3; d++ )
        {
            free( z[d] );
            lagrange_free( &ld[d] );
        }
        free( od_work );
    }

    // Gaussian quadrature points for a trilinear hex element.
    // Five 2d arrays are defined.
    // One for the single gaussian point solution, 2 point solution,
    // 3 point solution, 4 point solution and 5 point solution.
    // There are 2 columns, one for Weights and the other for Locations
    //                                Weight         Location

    const double gauss_1[1][2] = { { 2.0, 0.0 } };

    const double gauss_2[2][2] = { { 1.0, -0.5773502691 }, { 1.0, 0.5773502691 } };

    const double gauss_3[3][2] = { { 0.5555555555, -0.7745966692 },
                                   { 0.8888888888, 0.0 },
                                   { 0.5555555555, 0.7745966692 } };

    const double gauss_4[4][2] = { { 0.3478548451, -0.8611363116 },
                                   { 0.6521451549, -0.3399810436 },
                                   { 0.6521451549, 0.3399810436 },
                                   { 0.3478548451, 0.8611363116 } };

    const double gauss_5[5][2] = { { 0.2369268851, -0.9061798459 },
                                   { 0.4786286705, -0.5384693101 },
                                   { 0.5688888889, 0.0 },
                                   { 0.4786286705, 0.5384693101 },
                                   { 0.2369268851, 0.9061798459 } };

    // Function to integrate the field defined by field_fn function
    // over the volume of the trilinear hex defined by the hex_corners

    bool integrate_trilinear_hex( const CartVect* hex_corners, double* corner_fields, double& field_val, int num_pts )
    {
        // Create the LinearHexMap object using the hex_corners array of CartVects
        LinearHexMap hex( hex_corners );

        // Use the correct table of points and locations based on the num_pts parameter
        const double( *g_pts )[2] = 0;
        switch( num_pts )
        {
            case 1:
                g_pts = gauss_1;
                break;

            case 2:
                g_pts = gauss_2;
                break;

            case 3:
                g_pts = gauss_3;
                break;

            case 4:
                g_pts = gauss_4;
                break;

            case 5:
                g_pts = gauss_5;
                break;

            default:  // value out of range
                return false;
        }

        // Test code - print Gaussian Quadrature data
        if( debug )
        {
            for( int r = 0; r < num_pts; r++ )
                for( int c = 0; c < 2; c++ )
                    std::cout << "g_pts[" << r << "][" << c << "]=" << g_pts[r][c] << std::endl;
        }
        // End Test code

        double soln = 0.0;

        for( int i = 0; i < num_pts; i++ )
        {  // Loop for xi direction
            double w_i  = g_pts[i][0];
            double xi_i = g_pts[i][1];
            for( int j = 0; j < num_pts; j++ )
            {  // Loop for eta direction
                double w_j   = g_pts[j][0];
                double eta_j = g_pts[j][1];
                for( int k = 0; k < num_pts; k++ )
                {  // Loop for zeta direction
                    double w_k    = g_pts[k][0];
                    double zeta_k = g_pts[k][1];

                    // Calculate the "realType" space point given the "normal" point
                    CartVect normal_pt( xi_i, eta_j, zeta_k );

                    // Calculate the value of F(x(xi,eta,zeta),y(xi,eta,zeta),z(xi,eta,zeta)
                    double field = hex.evaluate_scalar_field( normal_pt, corner_fields );

                    // Calculate the Jacobian for this "normal" point and its determinant
                    Matrix3 J  = hex.jacobian( normal_pt );
                    double det = J.determinant();

                    // Calculate integral and update the solution
                    soln = soln + ( w_i * w_j * w_k * field * det );
                }
            }
        }

        // Set the output parameter
        field_val = soln;

        return true;
    }

}  // namespace ElemUtil

namespace Element
{

    Map::~Map() {}

    inline const std::vector< CartVect >& Map::get_vertices()
    {
        return this->vertex;
    }
    //
    void Map::set_vertices( const std::vector< CartVect >& v )
    {
        if( v.size() != this->vertex.size() )
        {
            throw ArgError();
        }
        this->vertex = v;
    }

    bool Map::inside_box( const CartVect& xi, double& tol ) const
    {
        // bail out early, before doing an expensive NR iteration
        // compute box
        BoundBox box( this->vertex );
        return box.contains_point( xi.array(), tol );
    }

    //
    CartVect Map::ievaluate( const CartVect& x, double tol, const CartVect& x0 ) const
    {
        // TODO: should differentiate between epsilons used for
        // Newton Raphson iteration, and epsilons used for curved boundary geometry errors
        // right now, fix the tolerance used for NR
        tol                        = 1.0e-10;
        const double error_tol_sqr = tol * tol;
        double det;
        CartVect xi    = x0;
        CartVect delta = evaluate( xi ) - x;
        Matrix3 J;

        int iters = 0;
        while( delta % delta > error_tol_sqr )
        {
            if( ++iters > 10 ) throw Map::EvaluationError( x, vertex );

            J   = jacobian( xi );
            det = J.determinant();
            if( det < std::numeric_limits< double >::epsilon() ) throw Map::EvaluationError( x, vertex );
            xi -= J.inverse() * delta;
            delta = evaluate( xi ) - x;
        }
        return xi;
    }  // Map::ievaluate()

    SphericalQuad::SphericalQuad( const std::vector< CartVect >& vertices ) : LinearQuad( vertices )
    {
        // project the vertices to the plane tangent at first vertex
        v1          = vertex[0];  // member data
        double v1v1 = v1 % v1;    // this is 1, in general, for unit sphere meshes
        for( int j = 1; j < 4; j++ )
        {
            // first, bring all vertices in the gnomonic plane
            //  the new vertex will intersect the plane at vnew
            //   so that (vnew-v1)%v1 is 0 ( vnew is in the tangent plane, i.e. normal to v1 )
            // pos is the old position of the vertex, and it is in general on the sphere
            // vnew = alfa*pos;  (alfa*pos-v1)%v1 = 0  <=> alfa*(pos%v1)=v1%v1 <=> alfa =
            // v1v1/(pos%v1)
            //  <=> vnew = ( v1v1/(pos%v1) )*pos
            CartVect vnew = v1v1 / ( vertex[j] % v1 ) * vertex[j];
            vertex[j]     = vnew;
        }
        // will compute a transf matrix, such that a new point will be transformed with
        // newpos =  transf * (vnew-v1), and it will be a point in the 2d plane
        // the transformation matrix will be oriented in such a way that orientation will be
        // positive
        CartVect vx = vertex[1] - v1;  // this will become Ox axis
        // z axis will be along v1, in such a way that orientation of the quad is positive
        // look at the first 2 edges
        CartVect vz = vx * ( vertex[2] - vertex[1] );
        vz          = vz / vz.length();

        vx = vx / vx.length();

        CartVect vy = vz * vx;
        transf      = Matrix3( vx[0], vx[1], vx[2], vy[0], vy[1], vy[2], vz[0], vz[1], vz[2] );
        vertex[0]   = CartVect( 0. );
        for( int j = 1; j < 4; j++ )
            vertex[j] = transf * ( vertex[j] - v1 );
    }

    CartVect SphericalQuad::ievaluate( const CartVect& x, double tol, const CartVect& x0 ) const
    {
        // project to the plane tangent at first vertex (gnomonic projection)
        double v1v1   = v1 % v1;
        CartVect vnew = v1v1 / ( x % v1 ) * x;  // so that (vnew-v1)%v1 is 0
        vnew          = transf * ( vnew - v1 );
        // det will be positive now
        return Map::ievaluate( vnew, tol, x0 );
    }

    bool SphericalQuad::inside_box( const CartVect& pos, double& tol ) const
    {
        // project to the plane tangent at first vertex
        // CartVect v1=vertex[0];
        double v1v1   = v1 % v1;
        CartVect vnew = v1v1 / ( pos % v1 ) * pos;  // so that (x-v1)%v1 is 0
        vnew          = transf * ( vnew - v1 );
        return Map::inside_box( vnew, tol );
    }

    const double LinearTri::corner[3][3] = { { 0, 0, 0 }, { 1, 0, 0 }, { 0, 1, 0 } };

    LinearTri::LinearTri() : Map( 0 ), det_T( 0.0 ), det_T_inverse( 0.0 ) {}  // LinearTri::LinearTri()

    LinearTri::~LinearTri() {}

    void LinearTri::set_vertices( const std::vector< CartVect >& v )
    {
        this->Map::set_vertices( v );
        this->T             = Matrix3( v[1][0] - v[0][0], v[2][0] - v[0][0], 0, v[1][1] - v[0][1], v[2][1] - v[0][1], 0,
                                       v[1][2] - v[0][2], v[2][2] - v[0][2], 1 );
        this->T_inverse     = this->T.inverse();
        this->det_T         = this->T.determinant();
        this->det_T_inverse = ( this->det_T < 1e-12 ? std::numeric_limits< double >::max() : 1.0 / this->det_T );
    }  // LinearTri::set_vertices()

    bool LinearTri::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // linear tri space is a triangle with vertices (0,0,0), (1,0,0), (0,1,0)
        // first check if outside bigger box, then below the line x+y=1
        return ( xi[0] >= -tol ) && ( xi[1] >= -tol ) && ( xi[2] >= -tol ) && ( xi[2] <= tol ) &&
               ( xi[0] + xi[1] < 1.0 + tol );
    }
    CartVect LinearTri::ievaluate( const CartVect& x, double /*tol*/, const CartVect& /*x0*/ ) const
    {
        return this->T_inverse * ( x - this->vertex[0] );
    }  // LinearTri::ievaluate

    double LinearTri::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_value ) const
    {
        double f0 = field_vertex_value[0];
        double f  = f0;
        for( unsigned i = 1; i < 3; ++i )
        {
            f += ( field_vertex_value[i] - f0 ) * xi[i - 1];
        }
        return f;
    }  // LinearTri::evaluate_scalar_field()

    double LinearTri::integrate_scalar_field( const double* field_vertex_values ) const
    {
        double I( 0.0 );
        for( unsigned int i = 0; i < 3; ++i )
        {
            I += field_vertex_values[i];
        }
        I *= this->det_T / 6.0;  // TODO
        return I;
    }  // LinearTri::integrate_scalar_field()

    SphericalTri::SphericalTri( const std::vector< CartVect >& vertices )
    {
        vertex.resize( vertices.size() );
        vertex = vertices;
        // project the vertices to the plane tangent at first vertex
        v1          = vertex[0];  // member data
        double v1v1 = v1 % v1;    // this is 1, in general, for unit sphere meshes
        for( int j = 1; j < 3; j++ )
        {
            // first, bring all vertices in the gnomonic plane
            //  the new vertex will intersect the plane at vnew
            //   so that (vnew-v1)%v1 is 0 ( vnew is in the tangent plane, i.e. normal to v1 )
            // pos is the old position of the vertex, and it is in general on the sphere
            // vnew = alfa*pos;  (alfa*pos-v1)%v1 = 0  <=> alfa*(pos%v1)=v1%v1 <=> alfa =
            // v1v1/(pos%v1)
            //  <=> vnew = ( v1v1/(pos%v1) )*pos
            CartVect vnew = v1v1 / ( vertex[j] % v1 ) * vertex[j];
            vertex[j]     = vnew;
        }
        // will compute a transf matrix, such that a new point will be transformed with
        // newpos =  transf * (vnew-v1), and it will be a point in the 2d plane
        // the transformation matrix will be oriented in such a way that orientation will be
        // positive
        CartVect vx = vertex[1] - v1;  // this will become Ox axis
        // z axis will be along v1, in such a way that orientation of the quad is positive
        // look at the first 2 edges
        CartVect vz = vx * ( vertex[2] - vertex[1] );
        vz          = vz / vz.length();

        vx = vx / vx.length();

        CartVect vy = vz * vx;
        transf      = Matrix3( vx[0], vx[1], vx[2], vy[0], vy[1], vy[2], vz[0], vz[1], vz[2] );
        vertex[0]   = CartVect( 0. );
        for( int j = 1; j < 3; j++ )
            vertex[j] = transf * ( vertex[j] - v1 );

        LinearTri::set_vertices( vertex );
    }

    CartVect SphericalTri::ievaluate( const CartVect& x, double /*tol*/, const CartVect& /*x0*/ ) const
    {
        // project to the plane tangent at first vertex (gnomonic projection)
        double v1v1   = v1 % v1;
        CartVect vnew = v1v1 / ( x % v1 ) * x;  // so that (vnew-v1)%v1 is 0
        vnew          = transf * ( vnew - v1 );
        // det will be positive now
        return LinearTri::ievaluate( vnew );
    }

    bool SphericalTri::inside_box( const CartVect& pos, double& tol ) const
    {
        // project to the plane tangent at first vertex
        // CartVect v1=vertex[0];
        double v1v1   = v1 % v1;
        CartVect vnew = v1v1 / ( pos % v1 ) * pos;  // so that (x-v1)%v1 is 0
        vnew          = transf * ( vnew - v1 );
        return Map::inside_box( vnew, tol );
    }

    // filescope for static member data that is cached
    const double LinearEdge::corner[2][3] = { { -1, 0, 0 }, { 1, 0, 0 } };

    LinearEdge::LinearEdge() : Map( 0 ) {}  // LinearEdge::LinearEdge()

    /* For each point, its weight and location are stored as an array.
       Hence, the inner dimension is 2, the outer dimension is gauss_count.
       We use a one-point Gaussian quadrature, since it integrates linear functions exactly.
    */
    const double LinearEdge::gauss[1][2] = { { 2.0, 0.0 } };

    CartVect LinearEdge::evaluate( const CartVect& xi ) const
    {
        CartVect x( 0.0 );
        for( unsigned i = 0; i < LinearEdge::corner_count; ++i )
        {
            const double N_i = ( 1.0 + xi[0] * corner[i][0] );
            x += N_i * this->vertex[i];
        }
        x /= LinearEdge::corner_count;
        return x;
    }  // LinearEdge::evaluate

    Matrix3 LinearEdge::jacobian( const CartVect& xi ) const
    {
        Matrix3 J( 0.0 );
        for( unsigned i = 0; i < LinearEdge::corner_count; ++i )
        {
            const double xi_p    = 1.0 + xi[0] * corner[i][0];
            const double dNi_dxi = corner[i][0] * xi_p;
            J( 0, 0 ) += dNi_dxi * vertex[i][0];
        }
        J( 1, 1 ) = 1.0; /* to make sure the Jacobian determinant is non-zero */
        J( 2, 2 ) = 1.0; /* to make sure the Jacobian determinant is non-zero */
        J /= LinearEdge::corner_count;
        return J;
    }  // LinearEdge::jacobian()

    double LinearEdge::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_value ) const
    {
        double f( 0.0 );
        for( unsigned i = 0; i < LinearEdge::corner_count; ++i )
        {
            const double N_i = ( 1 + xi[0] * corner[i][0] ) * ( 1.0 + xi[1] * corner[i][1] );
            f += N_i * field_vertex_value[i];
        }
        f /= LinearEdge::corner_count;
        return f;
    }  // LinearEdge::evaluate_scalar_field()

    double LinearEdge::integrate_scalar_field( const double* field_vertex_values ) const
    {
        double I( 0.0 );
        for( unsigned int j1 = 0; j1 < this->gauss_count; ++j1 )
        {
            double x1 = this->gauss[j1][1];
            double w1 = this->gauss[j1][0];
            CartVect x( x1, 0.0, 0.0 );
            I += this->evaluate_scalar_field( x, field_vertex_values ) * w1 * this->det_jacobian( x );
        }
        return I;
    }  // LinearEdge::integrate_scalar_field()

    bool LinearEdge::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol );
    }

    const double LinearHex::corner[8][3] = { { -1, -1, -1 }, { 1, -1, -1 }, { 1, 1, -1 }, { -1, 1, -1 },
                                             { -1, -1, 1 },  { 1, -1, 1 },  { 1, 1, 1 },  { -1, 1, 1 } };

    LinearHex::LinearHex() : Map( 0 ) {}  // LinearHex::LinearHex()

    LinearHex::~LinearHex() {}
    /* For each point, its weight and location are stored as an array.
       Hence, the inner dimension is 2, the outer dimension is gauss_count.
       We use a one-point Gaussian quadrature, since it integrates linear functions exactly.
    */
    // const double LinearHex::gauss[1][2] = { {  2.0,           0.0          } };
    const double LinearHex::gauss[2][2] = { { 1.0, -0.5773502691 }, { 1.0, 0.5773502691 } };
    // const double LinearHex::gauss[4][2] = { {  0.3478548451, -0.8611363116 },
    //                             {  0.6521451549, -0.3399810436 },
    //                             {  0.6521451549,  0.3399810436 },
    //                             {  0.3478548451,  0.8611363116 } };

    CartVect LinearHex::evaluate( const CartVect& xi ) const
    {
        CartVect x( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double N_i =
                ( 1 + xi[0] * corner[i][0] ) * ( 1 + xi[1] * corner[i][1] ) * ( 1 + xi[2] * corner[i][2] );
            x += N_i * this->vertex[i];
        }
        x *= 0.125;
        return x;
    }  // LinearHex::evaluate

    Matrix3 LinearHex::jacobian( const CartVect& xi ) const
    {
        Matrix3 J( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double xi_p      = 1 + xi[0] * corner[i][0];
            const double eta_p     = 1 + xi[1] * corner[i][1];
            const double zeta_p    = 1 + xi[2] * corner[i][2];
            const double dNi_dxi   = corner[i][0] * eta_p * zeta_p;
            const double dNi_deta  = corner[i][1] * xi_p * zeta_p;
            const double dNi_dzeta = corner[i][2] * xi_p * eta_p;
            J( 0, 0 ) += dNi_dxi * vertex[i][0];
            J( 1, 0 ) += dNi_dxi * vertex[i][1];
            J( 2, 0 ) += dNi_dxi * vertex[i][2];
            J( 0, 1 ) += dNi_deta * vertex[i][0];
            J( 1, 1 ) += dNi_deta * vertex[i][1];
            J( 2, 1 ) += dNi_deta * vertex[i][2];
            J( 0, 2 ) += dNi_dzeta * vertex[i][0];
            J( 1, 2 ) += dNi_dzeta * vertex[i][1];
            J( 2, 2 ) += dNi_dzeta * vertex[i][2];
        }
        return J *= 0.125;
    }  // LinearHex::jacobian()

    double LinearHex::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_value ) const
    {
        double f( 0.0 );
        for( unsigned i = 0; i < 8; ++i )
        {
            const double N_i =
                ( 1 + xi[0] * corner[i][0] ) * ( 1 + xi[1] * corner[i][1] ) * ( 1 + xi[2] * corner[i][2] );
            f += N_i * field_vertex_value[i];
        }
        f *= 0.125;
        return f;
    }  // LinearHex::evaluate_scalar_field()

    double LinearHex::integrate_scalar_field( const double* field_vertex_values ) const
    {
        double I( 0.0 );
        for( unsigned int j1 = 0; j1 < this->gauss_count; ++j1 )
        {
            double x1 = this->gauss[j1][1];
            double w1 = this->gauss[j1][0];
            for( unsigned int j2 = 0; j2 < this->gauss_count; ++j2 )
            {
                double x2 = this->gauss[j2][1];
                double w2 = this->gauss[j2][0];
                for( unsigned int j3 = 0; j3 < this->gauss_count; ++j3 )
                {
                    double x3 = this->gauss[j3][1];
                    double w3 = this->gauss[j3][0];
                    CartVect x( x1, x2, x3 );
                    I += this->evaluate_scalar_field( x, field_vertex_values ) * w1 * w2 * w3 * this->det_jacobian( x );
                }
            }
        }
        return I;
    }  // LinearHex::integrate_scalar_field()

    bool LinearHex::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol ) && ( xi[1] >= -1. - tol ) && ( xi[1] <= 1. + tol ) &&
               ( xi[2] >= -1. - tol ) && ( xi[2] <= 1. + tol );
    }

    // those are not just the corners, but for simplicity, keep this name
    //
    const int QuadraticHex::corner[27][3] = {
        { -1, -1, -1 }, { 1, -1, -1 }, { 1, 1, -1 },  // corner nodes: 0-7
        { -1, 1, -1 },                                // mid-edge nodes: 8-19
        { -1, -1, 1 },                                // center-face nodes 20-25  center node  26
        { 1, -1, 1 },                                 //
        { 1, 1, 1 },    { -1, 1, 1 },                 //                    4   ----- 19   -----  7
        { 0, -1, -1 },                                //                .   |                 .   |
        { 1, 0, -1 },                                 //            16         25         18      |
        { 0, 1, -1 },                                 //         .          |          .          |
        { -1, 0, -1 },                                //      5   ----- 17   -----  6             |
        { -1, -1, 0 },                                //      |            12       | 23         15
        { 1, -1, 0 },                                 //      |                     |             |
        { 1, 1, 0 },                                  //      |     20      |  26   |     22      |
        { -1, 1, 0 },                                 //      |                     |             |
        { 0, -1, 1 },                                 //     13         21  |      14             |
        { 1, 0, 1 },                                  //      |             0   ----- 11   -----  3
        { 0, 1, 1 },                                  //      |         .           |         .
        { -1, 0, 1 },                                 //      |      8         24   |     10
        { 0, -1, 0 },                                 //      |  .                  |  .
        { 1, 0, 0 },                                  //      1   -----  9   -----  2
        { 0, 1, 0 },                                  //
        { -1, 0, 0 },   { 0, 0, -1 },  { 0, 0, 1 },  { 0, 0, 0 } };
    // QuadraticHex::QuadraticHex(const std::vector<CartVect>& vertices) : Map(vertices){};
    QuadraticHex::QuadraticHex() : Map( 0 ) {}

    QuadraticHex::~QuadraticHex() {}
    double SH( const int i, const double xi )
    {
        switch( i )
        {
            case -1:
                return ( xi * xi - xi ) / 2;
            case 0:
                return 1 - xi * xi;
            case 1:
                return ( xi * xi + xi ) / 2;
            default:
                return 0.;
        }
    }
    double DSH( const int i, const double xi )
    {
        switch( i )
        {
            case -1:
                return xi - 0.5;
            case 0:
                return -2 * xi;
            case 1:
                return xi + 0.5;
            default:
                return 0.;
        }
    }

    CartVect QuadraticHex::evaluate( const CartVect& xi ) const
    {

        CartVect x( 0.0 );
        for( int i = 0; i < 27; i++ )
        {
            const double sh = SH( corner[i][0], xi[0] ) * SH( corner[i][1], xi[1] ) * SH( corner[i][2], xi[2] );
            x += sh * vertex[i];
        }

        return x;
    }

    bool QuadraticHex::inside_nat_space( const CartVect& xi, double& tol ) const
    {  // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol ) && ( xi[1] >= -1. - tol ) && ( xi[1] <= 1. + tol ) &&
               ( xi[2] >= -1. - tol ) && ( xi[2] <= 1. + tol );
    }

    Matrix3 QuadraticHex::jacobian( const CartVect& xi ) const
    {
        Matrix3 J( 0.0 );
        for( int i = 0; i < 27; i++ )
        {
            const double sh[3]  = { SH( corner[i][0], xi[0] ), SH( corner[i][1], xi[1] ), SH( corner[i][2], xi[2] ) };
            const double dsh[3] = { DSH( corner[i][0], xi[0] ), DSH( corner[i][1], xi[1] ),
                                    DSH( corner[i][2], xi[2] ) };

            for( int j = 0; j < 3; j++ )
            {
                J( j, 0 ) += dsh[0] * sh[1] * sh[2] * vertex[i][j];  // dxj/dr first column
                J( j, 1 ) += sh[0] * dsh[1] * sh[2] * vertex[i][j];  // dxj/ds
                J( j, 2 ) += sh[0] * sh[1] * dsh[2] * vertex[i][j];  // dxj/dt
            }
        }

        return J;
    }
    double QuadraticHex::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_values ) const
    {
        double x = 0.0;
        for( int i = 0; i < 27; i++ )
        {
            const double sh = SH( corner[i][0], xi[0] ) * SH( corner[i][1], xi[1] ) * SH( corner[i][2], xi[2] );
            x += sh * field_vertex_values[i];
        }

        return x;
    }
    double QuadraticHex::integrate_scalar_field( const double* /*field_vertex_values*/ ) const
    {
        return 0.;  // TODO: gaussian integration , probably 2x2x2
    }

    const double LinearTet::corner[4][3] = { { 0, 0, 0 }, { 1, 0, 0 }, { 0, 1, 0 }, { 0, 0, 1 } };

    LinearTet::LinearTet() : Map( 0 ), det_T( 0.0 ), det_T_inverse( 0.0 ) {}  // LinearTet::LinearTet()

    LinearTet::~LinearTet() {}

    void LinearTet::set_vertices( const std::vector< CartVect >& v )
    {
        this->Map::set_vertices( v );
        this->T =
            Matrix3( v[1][0] - v[0][0], v[2][0] - v[0][0], v[3][0] - v[0][0], v[1][1] - v[0][1], v[2][1] - v[0][1],
                     v[3][1] - v[0][1], v[1][2] - v[0][2], v[2][2] - v[0][2], v[3][2] - v[0][2] );
        this->T_inverse     = this->T.inverse();
        this->det_T         = this->T.determinant();
        this->det_T_inverse = ( this->det_T < 1e-12 ? std::numeric_limits< double >::max() : 1.0 / this->det_T );
    }  // LinearTet::set_vertices()

    double LinearTet::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_value ) const
    {
        double f0 = field_vertex_value[0];
        double f  = f0;
        for( unsigned i = 1; i < 4; ++i )
        {
            f += ( field_vertex_value[i] - f0 ) * xi[i - 1];
        }
        return f;
    }  // LinearTet::evaluate_scalar_field()

    CartVect LinearTet::ievaluate( const CartVect& x, double /*tol*/, const CartVect& /*x0*/ ) const
    {
        return this->T_inverse * ( x - this->vertex[0] );
    }  // LinearTet::ievaluate

    double LinearTet::integrate_scalar_field( const double* field_vertex_values ) const
    {
        double I( 0.0 );
        for( unsigned int i = 0; i < 4; ++i )
        {
            I += field_vertex_values[i];
        }
        I *= this->det_T / 24.0;
        return I;
    }  // LinearTet::integrate_scalar_field()
    bool LinearTet::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // linear tet space is a tetra with vertices (0,0,0), (1,0,0), (0,1,0), (0, 0, 1)
        // first check if outside bigger box, then below the plane x+y+z=1
        return ( xi[0] >= -tol ) && ( xi[1] >= -tol ) && ( xi[2] >= -tol ) && ( xi[0] + xi[1] + xi[2] < 1.0 + tol );
    }
    // SpectralHex

    // filescope for static member data that is cached
    int SpectralHex::_n;
    realType* SpectralHex::_z[3];
    lagrange_data SpectralHex::_ld[3];
    opt_data_3 SpectralHex::_data;
    realType* SpectralHex::_odwork;

    bool SpectralHex::_init = false;

    SpectralHex::SpectralHex() : Map( 0 )
    {
        _xyz[0] = _xyz[1] = _xyz[2] = NULL;
    }
    // the preferred constructor takes pointers to GL blocked positions
    SpectralHex::SpectralHex( int order, double* x, double* y, double* z ) : Map( 0 )
    {
        Init( order );
        _xyz[0] = x;
        _xyz[1] = y;
        _xyz[2] = z;
    }
    SpectralHex::SpectralHex( int order ) : Map( 0 )
    {
        Init( order );
        _xyz[0] = _xyz[1] = _xyz[2] = NULL;
    }
    SpectralHex::~SpectralHex()
    {
        if( _init ) freedata();
        _init = false;
    }
    void SpectralHex::Init( int order )
    {
        if( _init && _n == order ) return;
        if( _init && _n != order )
        {
            // TODO: free data cached
            freedata();
        }
        // compute stuff that depends only on order
        _init = true;
        _n    = order;
        // triplicates! n is the same in all directions !!!
        for( int d = 0; d < 3; d++ )
        {
            _z[d] = tmalloc( realType, _n );
            lobatto_nodes( _z[d], _n );
            lagrange_setup( &_ld[d], _z[d], _n );
        }
        opt_alloc_3( &_data, _ld );

        unsigned int nf = _n * _n, ne = _n, nw = 2 * _n * _n + 3 * _n;
        _odwork = tmalloc( realType, 6 * nf + 9 * ne + nw );
    }
    void SpectralHex::freedata()
    {
        for( int d = 0; d < 3; d++ )
        {
            free( _z[d] );
            lagrange_free( &_ld[d] );
        }
        opt_free_3( &_data );
        free( _odwork );
    }

    void SpectralHex::set_gl_points( double* x, double* y, double* z )
    {
        _xyz[0] = x;
        _xyz[1] = y;
        _xyz[2] = z;
    }
    CartVect SpectralHex::evaluate( const CartVect& xi ) const
    {
        // piece that we shouldn't want to cache
        int d = 0;
        for( d = 0; d < 3; d++ )
        {
            lagrange_0( &_ld[d], xi[d] );
        }
        CartVect result;
        for( d = 0; d < 3; d++ )
        {
            result[d] = tensor_i3( _ld[0].J, _ld[0].n, _ld[1].J, _ld[1].n, _ld[2].J, _ld[2].n,
                                   _xyz[d],  // this is the "field"
                                   _odwork );
        }
        return result;
    }
    // replicate the functionality of hex_findpt
    CartVect SpectralHex::ievaluate( CartVect const& xyz, double tol, const CartVect& x0 ) const
    {
        // find nearest point
        realType x_star[3];
        xyz.get( x_star );

        realType r[3] = { 0, 0, 0 };  // initial guess for parametric coords
        x0.get( r );
        unsigned c    = opt_no_constraints_3;
        realType dist = opt_findpt_3( &_data, (const realType**)_xyz, x_star, r, &c );
        // if it did not converge, get out with throw...
        if( dist > 10 * tol )  // outside the element
        {
            std::vector< CartVect > dummy;
            throw Map::EvaluationError( xyz, dummy );
        }
        // c tells us if we landed inside the element or exactly on a face, edge, or node
        // also, dist shows the distance to the computed point.
        // copy parametric coords back
        return CartVect( r );
    }
    Matrix3 SpectralHex::jacobian( const CartVect& xi ) const
    {
        realType x_i[3];
        xi.get( x_i );
        // set the positions of GL nodes, before evaluations
        _data.elx[0] = _xyz[0];
        _data.elx[1] = _xyz[1];
        _data.elx[2] = _xyz[2];
        opt_vol_set_intp_3( &_data, x_i );
        Matrix3 J( 0. );
        // it is organized differently
        J( 0, 0 ) = _data.jac[0];  // dx/dr
        J( 0, 1 ) = _data.jac[1];  // dx/ds
        J( 0, 2 ) = _data.jac[2];  // dx/dt
        J( 1, 0 ) = _data.jac[3];  // dy/dr
        J( 1, 1 ) = _data.jac[4];  // dy/ds
        J( 1, 2 ) = _data.jac[5];  // dy/dt
        J( 2, 0 ) = _data.jac[6];  // dz/dr
        J( 2, 1 ) = _data.jac[7];  // dz/ds
        J( 2, 2 ) = _data.jac[8];  // dz/dt
        return J;
    }
    double SpectralHex::evaluate_scalar_field( const CartVect& xi, const double* field ) const
    {
        // piece that we shouldn't want to cache
        int d;
        for( d = 0; d < 3; d++ )
        {
            lagrange_0( &_ld[d], xi[d] );
        }

        double value = tensor_i3( _ld[0].J, _ld[0].n, _ld[1].J, _ld[1].n, _ld[2].J, _ld[2].n, field, _odwork );
        return value;
    }
    double SpectralHex::integrate_scalar_field( const double* field_vertex_values ) const
    {
        // set the position of GL points
        // set the positions of GL nodes, before evaluations
        _data.elx[0] = _xyz[0];
        _data.elx[1] = _xyz[1];
        _data.elx[2] = _xyz[2];
        double xi[3];
        // triple loop; the most inner loop is in r direction, then s, then t
        double integral = 0.;
        // double volume = 0;
        int index = 0;  // used fr the inner loop
        for( int k = 0; k < _n; k++ )
        {
            xi[2] = _ld[2].z[k];
            // double wk= _ld[2].w[k];
            for( int j = 0; j < _n; j++ )
            {
                xi[1] = _ld[1].z[j];
                // double wj= _ld[1].w[j];
                for( int i = 0; i < _n; i++ )
                {
                    xi[0] = _ld[0].z[i];
                    // double wi= _ld[0].w[i];
                    opt_vol_set_intp_3( &_data, xi );
                    double wk = _ld[2].J[k];
                    double wj = _ld[1].J[j];
                    double wi = _ld[0].J[i];
                    Matrix3 J( 0. );
                    // it is organized differently
                    J( 0, 0 ) = _data.jac[0];  // dx/dr
                    J( 0, 1 ) = _data.jac[1];  // dx/ds
                    J( 0, 2 ) = _data.jac[2];  // dx/dt
                    J( 1, 0 ) = _data.jac[3];  // dy/dr
                    J( 1, 1 ) = _data.jac[4];  // dy/ds
                    J( 1, 2 ) = _data.jac[5];  // dy/dt
                    J( 2, 0 ) = _data.jac[6];  // dz/dr
                    J( 2, 1 ) = _data.jac[7];  // dz/ds
                    J( 2, 2 ) = _data.jac[8];  // dz/dt
                    double bm = wk * wj * wi * J.determinant();
                    integral += bm * field_vertex_values[index++];
                    // volume +=bm;
                }
            }
        }
        // std::cout << "volume: " << volume << "\n";
        return integral;
    }
    // this is the same as a linear hex, although we should not need it
    bool SpectralHex::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol ) && ( xi[1] >= -1. - tol ) && ( xi[1] <= 1. + tol ) &&
               ( xi[2] >= -1. - tol ) && ( xi[2] <= 1. + tol );
    }

    // SpectralHex

    // filescope for static member data that is cached
    const double LinearQuad::corner[4][3] = { { -1, -1, 0 }, { 1, -1, 0 }, { 1, 1, 0 }, { -1, 1, 0 } };

    LinearQuad::LinearQuad() : Map( 0 ) {}  // LinearQuad::LinearQuad()

    LinearQuad::~LinearQuad() {}

    /* For each point, its weight and location are stored as an array.
       Hence, the inner dimension is 2, the outer dimension is gauss_count.
       We use a one-point Gaussian quadrature, since it integrates linear functions exactly.
    */
    const double LinearQuad::gauss[1][2] = { { 2.0, 0.0 } };

    CartVect LinearQuad::evaluate( const CartVect& xi ) const
    {
        CartVect x( 0.0 );
        for( unsigned i = 0; i < LinearQuad::corner_count; ++i )
        {
            const double N_i = ( 1 + xi[0] * corner[i][0] ) * ( 1 + xi[1] * corner[i][1] );
            x += N_i * this->vertex[i];
        }
        x /= LinearQuad::corner_count;
        return x;
    }  // LinearQuad::evaluate

    Matrix3 LinearQuad::jacobian( const CartVect& xi ) const
    {
        // this basically ignores the z component: xi[2] or vertex[][2]
        Matrix3 J( 0.0 );
        for( unsigned i = 0; i < LinearQuad::corner_count; ++i )
        {
            const double xi_p     = 1 + xi[0] * corner[i][0];
            const double eta_p    = 1 + xi[1] * corner[i][1];
            const double dNi_dxi  = corner[i][0] * eta_p;
            const double dNi_deta = corner[i][1] * xi_p;
            J( 0, 0 ) += dNi_dxi * vertex[i][0];
            J( 1, 0 ) += dNi_dxi * vertex[i][1];
            J( 0, 1 ) += dNi_deta * vertex[i][0];
            J( 1, 1 ) += dNi_deta * vertex[i][1];
        }
        J( 2, 2 ) = 1.0; /* to make sure the Jacobian determinant is non-zero */
        J /= LinearQuad::corner_count;
        return J;
    }  // LinearQuad::jacobian()

    double LinearQuad::evaluate_scalar_field( const CartVect& xi, const double* field_vertex_value ) const
    {
        double f( 0.0 );
        for( unsigned i = 0; i < LinearQuad::corner_count; ++i )
        {
            const double N_i = ( 1 + xi[0] * corner[i][0] ) * ( 1 + xi[1] * corner[i][1] );
            f += N_i * field_vertex_value[i];
        }
        f /= LinearQuad::corner_count;
        return f;
    }  // LinearQuad::evaluate_scalar_field()

    double LinearQuad::integrate_scalar_field( const double* field_vertex_values ) const
    {
        double I( 0.0 );
        for( unsigned int j1 = 0; j1 < this->gauss_count; ++j1 )
        {
            double x1 = this->gauss[j1][1];
            double w1 = this->gauss[j1][0];
            for( unsigned int j2 = 0; j2 < this->gauss_count; ++j2 )
            {
                double x2 = this->gauss[j2][1];
                double w2 = this->gauss[j2][0];
                CartVect x( x1, x2, 0.0 );
                I += this->evaluate_scalar_field( x, field_vertex_values ) * w1 * w2 * this->det_jacobian( x );
            }
        }
        return I;
    }  // LinearQuad::integrate_scalar_field()

    bool LinearQuad::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol ) && ( xi[1] >= -1. - tol ) && ( xi[1] <= 1. + tol );
    }

    // filescope for static member data that is cached
    int SpectralQuad::_n;
    realType* SpectralQuad::_z[2];
    lagrange_data SpectralQuad::_ld[2];
    opt_data_2 SpectralQuad::_data;
    realType* SpectralQuad::_odwork;
    realType* SpectralQuad::_glpoints;
    bool SpectralQuad::_init = false;

    SpectralQuad::SpectralQuad() : Map( 0 )
    {
        _xyz[0] = _xyz[1] = _xyz[2] = NULL;
    }
    // the preferred constructor takes pointers to GL blocked positions
    SpectralQuad::SpectralQuad( int order, double* x, double* y, double* z ) : Map( 0 )
    {
        Init( order );
        _xyz[0] = x;
        _xyz[1] = y;
        _xyz[2] = z;
    }
    SpectralQuad::SpectralQuad( int order ) : Map( 4 )
    {
        Init( order );
        _xyz[0] = _xyz[1] = _xyz[2] = NULL;
    }
    SpectralQuad::~SpectralQuad()
    {
        if( _init ) freedata();
        _init = false;
    }
    void SpectralQuad::Init( int order )
    {
        if( _init && _n == order ) return;
        if( _init && _n != order )
        {
            // TODO: free data cached
            freedata();
        }
        // compute stuff that depends only on order
        _init = true;
        _n    = order;
        // duplicates! n is the same in all directions !!!
        for( int d = 0; d < 2; d++ )
        {
            _z[d] = tmalloc( realType, _n );
            lobatto_nodes( _z[d], _n );
            lagrange_setup( &_ld[d], _z[d], _n );
        }
        opt_alloc_2( &_data, _ld );

        unsigned int nf = _n * _n, ne = _n, nw = 2 * _n * _n + 3 * _n;
        _odwork   = tmalloc( realType, 6 * nf + 9 * ne + nw );
        _glpoints = tmalloc( realType, 3 * nf );
    }

    void SpectralQuad::freedata()
    {
        for( int d = 0; d < 2; d++ )
        {
            free( _z[d] );
            lagrange_free( &_ld[d] );
        }
        opt_free_2( &_data );
        free( _odwork );
        free( _glpoints );
    }

    void SpectralQuad::set_gl_points( double* x, double* y, double* z )
    {
        _xyz[0] = x;
        _xyz[1] = y;
        _xyz[2] = z;
    }
    CartVect SpectralQuad::evaluate( const CartVect& xi ) const
    {
        // piece that we shouldn't want to cache
        int d = 0;
        for( d = 0; d < 2; d++ )
        {
            lagrange_0( &_ld[d], xi[d] );
        }
        CartVect result;
        for( d = 0; d < 3; d++ )
        {
            result[d] = tensor_i2( _ld[0].J, _ld[0].n, _ld[1].J, _ld[1].n, _xyz[d], _odwork );
        }
        return result;
    }
    // replicate the functionality of hex_findpt
    CartVect SpectralQuad::ievaluate( CartVect const& xyz, double /*tol*/, const CartVect& /*x0*/ ) const
    {
        // find nearest point
        realType x_star[3];
        xyz.get( x_star );

        realType r[2] = { 0, 0 };  // initial guess for parametric coords
        unsigned c    = opt_no_constraints_3;
        realType dist = opt_findpt_2( &_data, (const realType**)_xyz, x_star, r, &c );
        // if it did not converge, get out with throw...
        if( dist > 0.9e+30 )
        {
            std::vector< CartVect > dummy;
            throw Map::EvaluationError( xyz, dummy );
        }

        // c tells us if we landed inside the element or exactly on a face, edge, or node
        // also, dist shows the distance to the computed point.
        // copy parametric coords back
        return CartVect( r[0], r[1], 0. );
    }

    Matrix3 SpectralQuad::jacobian( const CartVect& /*xi*/ ) const
    {
        // not implemented
        Matrix3 J( 0. );
        return J;
    }

    double SpectralQuad::evaluate_scalar_field( const CartVect& xi, const double* field ) const
    {
        // piece that we shouldn't want to cache
        int d;
        for( d = 0; d < 2; d++ )
        {
            lagrange_0( &_ld[d], xi[d] );
        }

        double value = tensor_i2( _ld[0].J, _ld[0].n, _ld[1].J, _ld[1].n, field, _odwork );
        return value;
    }
    double SpectralQuad::integrate_scalar_field( const double* /*field_vertex_values*/ ) const
    {
        return 0.;  // not implemented
    }
    // this is the same as a linear hex, although we should not need it
    bool SpectralQuad::inside_nat_space( const CartVect& xi, double& tol ) const
    {
        // just look at the box+tol here
        return ( xi[0] >= -1. - tol ) && ( xi[0] <= 1. + tol ) && ( xi[1] >= -1. - tol ) && ( xi[1] <= 1. + tol );
    }
    // something we don't do for spectral hex; we do it here because
    //       we do not store the position of gl points in a tag yet
    void SpectralQuad::compute_gl_positions()
    {
        // will need to use shape functions on a simple linear quad to compute gl points
        // so we know the position of gl points in parametric space, we will just compute those
        // from the 3d vertex position (corner nodes of the quad), using simple mapping
        assert( this->vertex.size() == 4 );
        static double corner_xi[4][2] = { { -1., -1. }, { 1., -1. }, { 1., 1. }, { -1., 1. } };
        // we will use the cached lobatto nodes in parametric space _z[d] (the same in both
        // directions)
        int indexGL = 0;
        int n2      = _n * _n;
        for( int i = 0; i < _n; i++ )
        {
            double eta = _z[0][i];
            for( int j = 0; j < _n; j++ )
            {
                double csi = _z[1][j];  // we could really use the same _z[0] array of lobatto nodes
                CartVect pos( 0.0 );
                for( int k = 0; k < 4; k++ )
                {
                    const double N_k = ( 1 + csi * corner_xi[k][0] ) * ( 1 + eta * corner_xi[k][1] );
                    pos += N_k * vertex[k];
                }
                pos *= 0.25;                           // these are x, y, z of gl points; reorder them
                _glpoints[indexGL]          = pos[0];  // x
                _glpoints[indexGL + n2]     = pos[1];  // y
                _glpoints[indexGL + 2 * n2] = pos[2];  // z
                indexGL++;
            }
        }
        // now, we can set the _xyz pointers to internal memory allocated to these!
        _xyz[0] = &( _glpoints[0] );
        _xyz[1] = &( _glpoints[n2] );
        _xyz[2] = &( _glpoints[2 * n2] );
    }
    void SpectralQuad::get_gl_points( double*& x, double*& y, double*& z, int& psize )
    {
        x     = (double*)_xyz[0];
        y     = (double*)_xyz[1];
        z     = (double*)_xyz[2];
        psize = _n * _n;
    }
}  // namespace Element

}  // namespace moab