function [k,dof] = truss2k(nodes,n1,n2,A,E)
%
%  Return an element stiffness matrix (global coord.)
%  and a DOF list
%
%  nodes -- list of all node coord.
%  n1, n2 -- node numbers for this elem
%  A -- cross-section area
%  E -- modulus of elasticity
%
%  k -- element stiffness matrix, global coord.
%  dof -- global DOF list
%
error(nargchk(5,5,nargin));  %% 5 inputs req'd
if n1==n2
   error('Distinct node numbers required')
end
x1 = 
y1 = 
x2 = 
y2 = 
dx = x2-x1;
dy = y2-y1;
len = sqrt(dx^2 + dy^2);
if len==0
   error('Zero length element');
end
theta = 
%
%  Eq. 3.1.14
%
khat = (A*E/len) * [1 -1
                   -1  1];
C = cos(theta);
S = sin(theta);
%
%  Eq. 3.4.8
%
Tstar = 

%
%  Eq. 3.4.22
%
k = 
%
%  DOF list, see writeup
%
dof = [2*n1-1 2*n1 2*n2-1 2*n2];