function [kc,kh] = rodtk(nodes,n1,n2,Kxx,A,hP)
%function [kc,kh] = rodtk(nodes,n1,n2,Kxx,A,hP)
%
%  Generate thermal conductivity element for 1-D rod element
%
%  nodes = list of all nodes
%  n1, n2 = node numbers
%  Kxx = thermal conductivity
%  A = cross-section area
%  h = optional convection coefficient times perimeter
%
%  k = conductivity matrix 2x2
%
error(nargchk(5,6,nargin));
L = nodes(n2,1) - nodes(n1,1);
kc = (A*Kxx/L) * [1 -1        %% eq. 13.4.20 (typo in book)
                 -1  1];
if nargin > 5
    kh = (hP/6)*[2  1
                 1  2];
else
    kh = [];
end