function [Ke]=bar2g(ex,ey,ep,N)% Ke=bar2g(ex,ey,ep,N)%----------------------------------------------------------------% PURPOSE%  Compute element stiffness matrix for two dimensional geometric%  nonlinear bar element.%% INPUT:  ex = [x1 x2]%         ey = [y1 y2]       element node coordinates%%         ep = [E A]         E: Young's modulus%                            A: Cross section area%%         N                  normal force%% OUTPUT: Ke :   stiffness matrix, dim(Ke)= 4 x 4%----------------------------------------------------------------% LAST MODIFIED: K Persson    1995-08-23% Copyright (c)  Division of Structural Mechanics and%                Department of Solid Mechanics.%                Lund Institute of Technology%----------------------------------------------------------------   E=ep(1);   A=ep(2);    b=[ ex(2)-ex(1); ey(2)-ey(1) ];   L=sqrt(b'*b);   n=b'/L;  G=[n(1) n(2)  0   0   ;              -n(2) n(1)  0   0   ;                0    0   n(1) n(2);                0    0  -n(2) n(1)];   Kle=E*A/L*[1  0 -1  0;              0  0  0  0;             -1  0  1  0;              0  0  0  0] + N/L*[0  0  0  0;                                 0  1  0 -1;                                 0  0  0  0;                                 0 -1  0  1];   Ke=G'*Kle*G;%--------------------------end--------------------------------