k4 = h * deriv(t + h/2.0, x + k1/8.0 + (3.0/8.0)*k3);
See class notes on Runge-Kutta
Matrix k4 = deriv(t + h/2.0, x.plus(k1.times(0.125)).plus(k3.times(0.375))).times(h);
See Jama documentation.
Maintained by John Loomis, last updated 6 April 2019