log likelihood and derivatives for Gamma distribution
llikGamma(x, shape, rate, full = FALSE)data frame with fx for the log pdf value of with dProb
that has the derivatives with respect to the prob parameters at
the observation time-point
llikGamma(1, 1, 10)
#> fx dShape dRate
#> 1 -7.697415 2.879801 -0.9