sigmoid_length: Length based sigmoid selectivity function

In sizespectrum/mizer: Dynamic Multi-Species Size Spectrum Modelling

Length based sigmoid selectivity function

Description

A sigmoid shaped selectivity function. Based on two parameters l25 and l50 which determine the length at which 25% and 50% of the stock is selected respectively.

Usage

sigmoid_length(w, l25, l50, species_params, ...)

Arguments

w	Vector of sizes.
l25	the length which gives a selectivity of 25%.
l50	the length which gives a selectivity of 50%.
species_params	A list with the species params for the current species. Used to get at the length-weight parameters a and b.
...	Unused

Details

The selectivity is given by the logistic function

S(l) = \frac{1}{1 + \exp\left(\log(3)\frac{l50 -l}{l50 - l25}\right)}

As the mizer model is weight based, and this selectivity function is length based, it uses the length-weight parameters a and b to convert between length and weight

l = \left(\frac{w}{a}\right)^{1/b}

Value

Vector of selectivities at the given sizes.

See Also

gear_params() for setting the selectivity parameters.

Other selectivity functions: double_sigmoid_length(), knife_edge(), sigmoid_weight()

sizespectrum/mizer documentation built on April 14, 2024, 3:08 a.m.