base/ElemStiffMat2DP1.m

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function AElem=ElemStiffMat2DP1(q1,q2,q3,area)
% function AElem=ElemStiffMat2DP1(q1,q2,q3,area)
%   Computation of the element stiffness matrix for
%  `P_1`-Lagrange finite elements
%
% Parameters:
%  q1: Coordinates of the first vertex in the triangle,  `2\times 1` array 
%  q2: Coordinates of the second vertex in the triangle, `2\times 1` array 
%  q3: Coordinates of the third vertex in the triangle,  `2\times 1` array 
%  area: triangle area
%
% Return values:
%  AElem: Element stiffness matrix, `3\times 3` matrix
%
% Example:
%  @verbatim 
%    q1=[0;0];q2=[0;1];q3=[1;0];
%    area=1/2.;
%    AElem=ElemStiffMat2DP1(q1,q2,q3,area);
%  @endverbatim
% Copyright:
%   See \ref license
M=[q2-q3, q3-q1, q1-q2];
AElem=(1/(4*area))*M'*M;