An internal function to compute next Y based on continous-time model (Yashin et. al., 2007)
getNextY.cont(y1, t1, t2, a, f1, Q, f, b, theta)
y.next Next value of Y
y1
t1
t2
a (see Yashin et. al, 2007)
f1 (see Yashin et. al, 2007)
Q (see Yashin et. al, 2007)
f (see Yashin et. al, 2007)
b (see Yashin et. al, 2007)
theta (see Yashin et. al, 2007)