For deriv = 0, the log of theta, i.e.,
log(1-theta) when inverse = FALSE,
and if inverse = TRUE then
1-exp(theta).
For deriv = 1, then the function returns
deta / dtheta as a function of theta
if inverse = FALSE,
else if inverse = TRUE then it returns the reciprocal.
Here, all logarithms are natural logarithms, i.e., to base e.
Details
The complementary-log link function is suitable for parameters that
are less than unity.
Numerical values of theta close to 1 or out of range
result in
Inf, -Inf, NA or NaN.
References
McCullagh, P. and Nelder, J. A. (1989)
Generalized Linear Models, 2nd ed. London: Chapman & Hall.