fn_Create_Truss_Poly.hpp

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/*
 * BELFEM -- The Berkeley Lab Finite Element Framework
 * Copyright (c) 2026, The Regents of the University of California,
 * through Lawrence Berkeley National Laboratory (subject to receipt of any required
 * approvals from the U.S. Dept. of Energy).  All rights reserved.
 *
 * Developers: Christian Messe, Gregory Giard
 *
 * See the top-level LICENSE file for the complete license and disclaimer.
 */
 
#ifndef BELFEM_FN_CREATE_CUBE_HPP
#define BELFEM_FN_CREATE_CUBE_HPP
 
#include "typedefs.hpp"
#include "cl_Vector.hpp"
namespace belfem
{

    template < typename  T >
    void
    create_truss_poly(
            const Vector< T > & aX,
            const Vector< T > & aF,
                  Vector< T > & aC )
    {
        // help variable
        real tG = aX( 0 ) - aX( 1 );
        real tH = aX( 0 ) + aX( 1 );
 
        aC.set_size( 4 );
 
        // a
        aC( 0 ) = ( 2.0*( aF( 2 ) - aF( 0 ) ) + (aF( 1 ) + aF( 3 ) )* tG )*tG;
 
        // b
        aC( 1 ) = tG * (3*tH*( aF( 0 ) - aF( 2 ) ) - tG*( aF( 1 )*aX( 0 )
                  + 2.0*( aF( 3 )*aX( 0 ) + aF( 1 )*aX( 1 ) ) + aF( 3 )*aX( 1 ) ) );
 
        // c
        aC( 2 ) = tG * ( aF( 3 )*std::pow( aX( 0 ), 3 ) + aX( 0 )*aX( 1 )*(
                  6.0 * ( aF( 2 ) - aF( 0 ) ) +
                  aX( 0 ) * ( 2.0 * aF( 1 ) + aF( 3 ) )
        - aX( 1 ) * (aF( 1 ) + 2.0 * aF( 3 ) ) ) - aF( 1 )*std::pow( aX( 1 ), 3 ) );
 
        // d
        aC( 3 ) = tG * ( std::pow( aX( 0 ), 2 )
                *( aF( 2 )*(aX( 0 ) - 3.0*aX( 1 )) - tG*aX( 1 )*aF( 3 ) )
                  - std::pow( aX( 1 ), 2 ) *( aF( 0 )*(aX( 1 ) - 3.0*aX( 0 ) )
                  + tG*aX( 0 )*aF( 1 ) ) );
 
        // scale parameters to correct size
        aC *= std::pow( tG, -4 );
    }
}
#endif //BELFEM_FN_CREATE_CUBE_HPP