A sharkfin function is built in steps:
take the product of two sigmoidal functions
the first one rises around day \(D\) with rate parameter \(uk\)
the second one decays around day \(D+L\) with rate \(-dk\)
the product is raised a power \(pw\)
the result is scaled so that the maximum is \(mx\) For the default values, the function looks like a shark fin.
Usage
# S3 method for class 'sharkfin'
make_function(opts)