threshold_f.Rd
Generic threshold F harvest control rule #' A generic 4 parameters threshold F HCR.
threshold_f(x, f_min, f_max, lrp, urp)
input to HCR (e.g. SSB or, SSB/B40)
F to use when x < lrp
F to use when x > urp
value of x below which f_min applies
value of x above which f_max applies
fishing mortality rate