dx1/dt = k5*x2 + k4*x2 - k6*x1*x6; dx2/dt = -k5*x2 - k4*x2 + k6*x1*x6; dx3/dt = -k3*x3 - k2*x3 + k1*x5*x4; dx4/dt = k3*x3 + k2*x3 + k1*x5*x4; dx5/dt = k4*x2 + k2*x3 - k1*x5*x4; dx6/dt = k5*x2 + k3*x3 - k6*x1*x6; y1 = x6; y2 = x4