Description

SF_SIMP_RT1 Linear vector (Raviart-Thomas) divergence shape function for simplices.

[ VBASE, NLDOF, XLDOF, SFUN ] = SF_SIMP_RT1( I_EVAL, N_SDIM, N_VERT, I_DOF, XI, AINVJAC, VBASE ) Evaluates linear vector Raviart-Thomas divergence shape functions on simplices with values defined in the nodes. XI is Barycentric coordinates.

Input       Value/[Size]           Description
-----------------------------------------------------------------------------------
i_eval      scalar:  1             Evaluate function values
                    >1             Evaluate values of derivatives
n_sdim      scalar: 2/3            Number of space dimensions
n_vert      scalar: 3/4            Number of vertices per cell
i_dof       scalar: 1-n_ldof       Local basis function to evaluate
xi          [n_sdim+1]             Local coordinates of evaluation point
aInvJac     [n,n_sdim+1*n_sdim]    Inverse of transformation Jacobian
vBase       [n,1,2/3]              Preallocated output vector
                                                                                  .
Output      Value/[Size]           Description
-----------------------------------------------------------------------------------
vBase       [n,1,2/3]              Evaluated function values
nLDof       [4]                    Number of local degrees of freedom on
                                   vertices, edges, faces, and cell interiors
xLDof       [n_sdim,n_ldof]        Local coordinates of local dofs
sfun        string                 Function name of called shape function

Code listing

 sfun = 'sf_simp_RT1';
 if( n_sdim~=2 )
   error( [sfun,': shape function only defined in 2D.'] )
 end

 if( n_sdim==2 )
   nLDof = [0 3 0 0];
   xLDof = [1/2 0   1/2;
            1/2 1/2 0  ;
            0   1/2 1/2];
 else
   nLDof = [0 0 4 0];
   xLDof = [1/3 1/3   0 1/3;
            1/3 1/3 1/3   0;
            1/3   0 1/3 1/3;
            0 1/3 1/3   1/3];
 end


 switch i_eval    % Evaluation type flag.

   case 1         % Evaluation of function values.

     if( n_sdim==2 )
       j_dof = mod(i_dof,3) + 1;

       vBase = cat( 3,  xi(i_dof)*aInvJac(:,j_dof+n_vert) - xi(j_dof)*aInvJac(:,i_dof+n_vert), ...
                       -xi(i_dof)*aInvJac(:,j_dof)        + xi(j_dof)*aInvJac(:,i_dof) );

     end

   case {2,3,4}   % Evaluation of first derivatives.

     if( n_sdim==2 )

       j_dof = mod(i_dof,3) + 1;

       dNdxii1 =  aInvJac(:,j_dof+n_vert);
       dNdxij1 = -aInvJac(:,i_dof+n_vert);

       dNdxii2 = -aInvJac(:,j_dof);
       dNdxij2 =  aInvJac(:,i_dof);

       vBase = cat( 3, ( aInvJac(:,i_dof+3*(i_eval-2)).*dNdxii1 + aInvJac(:,j_dof+3*(i_eval-2)).*dNdxij1 ), ...
                       ( aInvJac(:,i_dof+3*(i_eval-2)).*dNdxii2 + aInvJac(:,j_dof+3*(i_eval-2)).*dNdxij2 ) );

     end

   case {5}   % Evaluation of divergence.

     if( n_sdim==2 )

       j_dof = mod(i_dof,3) + 1;

       dNdxii1 =  aInvJac(:,j_dof+n_vert);
       dNdxij1 = -aInvJac(:,i_dof+n_vert);

       dNdxii2 = -aInvJac(:,j_dof);
       dNdxij2 =  aInvJac(:,i_dof);

       vBase = ( aInvJac(:,i_dof)  .*dNdxii1 + aInvJac(:,j_dof)  .*dNdxij1 ) + ...
               ( aInvJac(:,i_dof+3).*dNdxii2 + aInvJac(:,j_dof+3).*dNdxij2 );

     end

   otherwise
     vBase = 0;

 end