function xdot = vdpol(t,x)% define variablesglobal C alpha ts A B a offset X%for i=1:42% if (x(i) < 0)%  disp('alert')% end%nd% set up differential equation matrixxdot = zeros(42,1);xdot(1) = x(1)*A + x(2)*B;% DE for instantenous queue lengthK=0;for i=1:40   K = K + x(offset+i)./(a(offset+i) + x(2)./C);endxdot(2) = -1.0*C +  K;% DE for individual flowsoffset = 2;     % because the first 2 DE are x and qfor i=1:40  xdot(i+offset) = 1.0/(a(i+offset)+x(2)./C) - p(x(1)).*x(i+offset).*x(i+offset)./(2.0*(a(i+offset)+x(2)./C));end% adjustmentif (x(1)+xdot(1) < 0.0)      xdot(1) = -1.0*x(1);endif (x(2)+xdot(2) < 0.0)      xdot(2) = -1.0*x(2);endfor i=1:40if (x(i+offset)+xdot(i+offset) < 0.0)      xdot(i+offset) = -1.0*x(i+offset);endend