Evaluates the supIG trawl function
trawl_supIG(x, delta, gamma)the argument at which the supIG trawl function will be evaluated
the parameter \(\delta\) in the supIG trawl
the parameter \(\gamma\) in the supIG trawl
The supIG trawl function evaluated at x
The trawl function is parametrised by the two parameters \(\delta \geq 0\) and \(\gamma \geq 0\) as follows: $$gd(x) = (1-2x\gamma^{-2})^{-1/2}\exp(\delta \gamma(1-(1-2x\gamma^{-2})^{1/2})), \mbox{ for } x \le 0.$$ It is assumed that \(\delta\) and \(\gamma\) are not simultaneously equal to zero.