The function returns the value of the ETAS triggering function at a specified time t for the points in the history th, mh
Details
The ETAS triggering function to be evaluated is
$$g(t - t_h | m_h) = K e^{\alpha(m_h - M_0)} \left( \frac{t - t_h}{c} + 1\right)^{-p}$$
Where \(K, \alpha, c > 0\), and \(p \geq 1\) are the ETAS parameters, \(t\) (t) is the time
at which the function is evaluated, considering the past observation \(t_h, m_h\) (th, mh).
The function returns 0 if \(t_h > t\).
If \(t\) is a scalar and \(t_h, m_h\) are vectors than the function returns a vector,
same if \(t\) is a vector and \(t_h, m_h\) are scalars, or if \(t, t_h, m_h\) are vectors of the same length.
Do not use if \(t\) and \(t_h, m_h\) are vectors of different lengths.