StiffElasAssembling3DP1base.m

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function K=StiffElasAssembling3DP1base(nq,nme,q,me,volumes,lambda,mu,Num)
% function K=StiffElasAssembling3DP1base(nq,nme,q,me,volumes,lambda,mu,Num)
%   Assembly of the Stiffness Elasticity Matrix by `P_1`-Lagrange finite elements in 3D
%   using basic version (see report).
%
%   The Stiffness Elasticity Matrix is given by 
%   ``\StiffElas_{m,l}=\int_{\DOMH} \Odv^t(\BasisFuncTwoD_m) \Ocv(\BasisFuncTwoD_l)dT, \ \forall (m,l)\in\ENS{1}{2\,\nq}^2,``
%   where `\BasisFuncTwoD_m` are `P_1`-Lagrange vector basis functions.
%   Here `\Ocv=(\Occ_{xx},\Occ_{yy},\Occ_{zz}, \Occ_{xy}, \Occ_{yz}, \Occ_{xz})^t` and 
%        `\Odv=(\Odc_{xx},\Odc_{yy},\Odc_{zz},2\Odc_{xy},2\Odc_{yz},2\Odc_{xz})^t`
%   are the elastic stress and strain tensors respectively. 
%
% Parameters:
%  nq: total number of vertices, also denoted by `\nq`.
%  nme: total number of elements, also denoted by `\nme`.
%  q: Array of vertices coordinates, `3\times\nq` array. <br/>
%  `{\q}(\il,j)` is the
%  `\il`-th coordinate of the `j`-th vertex, `\il\in\{1,2,3\}` and
%  `j\in\ENS{1}{\nq}`
%  me: Connectivity array, `4\times\nme` array. <br/>
%  `\me(\jl,k)` is the storage index of the
%  `\jl`-th  vertex of the `k`-th tetrahedron in the array `\q` of vertices coordinates, `\jl\in\{1,2,3,4\}` and
%       `k\in{\ENS{1}{\nme}}`.
%  volumes: Array of volumes, `1\times\nme array`. volumes(k) is the volume
%         of the k-th tetrahedron.
%  lambda: the first Lame coefficient in Hooke's law
%  mu: the second Lame coefficient in Hooke's law
%  Num: 
%    - 0 global alternate numbering with local alternate numbering (classical method), 
%    - 1 global block numbering with local alternate numbering,
%    - 2 global alternate numbering with local block numbering,
%    - 3 global block numbering with local block numbering.
%
% Return values:
%  K: `3\nq\times 3\nq` stiffness elasticity sparse matrix
%
% Example:
%  @verbatim 
%    Th=CubeMesh(10);
%    KK=StiffElasAssembling3DP1base(Th.nq,Th.nme,Th.q,Th.me,Th.areas,1.,0.25,0);@endverbatim
%  
% See also:
%   #BuildIkFunc, #BuildElemStiffElasMatFunc
% Copyright:
%   See \ref license
K=sparse(3*nq,3*nq);
GetI=BuildIkFunc(Num,nq);
H=Hooke(lambda,mu);
ElemStiffElasMat=BuildElemStiffElasMatFunc(Num);
for k=1:nme
    E=ElemStiffElasMat(q(:,me(:,k)),volumes(k),H);
    I=GetI(me,k);
    for il=1:12
        for jl=1:12
            K(I(il),I(jl))=K(I(il),I(jl))+E(il,jl);
        end
    end
end