Computes $g_i = exp(-alpha3 * sum_{j<i} 1[ ||x_i-x_j|| <= beta3 AND (t_i - t_j) >= gamma3 ])$ for i = 1..n, with g_0 = exp(0) = 1.
interaction_st_fast(data, params)NumericVector length n of exp(-alpha3 * counts)
NumericMatrix with columns (time, x, y). Assumed sorted by time ascending.
NumericVector length 3: (alpha3, beta3, gamma3)