logist {MQMF}

logist Logistic selectivity function

Description

logist calculates a Logistic curve that can be used as a selectivity function, or maturity curve, or wherever a logistic is required. This version uses the logistic function 1/(1+exp(-log(19.0)*(lens-inL50)/delta)), which explicitly defines the L50 and uses delta = (inL95-inL50) as the second parameter.

Usage

logist(inL50, delta, depend, knifeedge = FALSE)

Arguments

inL50

length at 50 percent the maximum selection/maturity/whatever

delta

is the difference in selection/maturity/whatever between inL50 and inL95 (inL95 = length at 95 percent of maximum)

depend

a vector of lengths/ages for which the logistic value will be calculated.

knifeedge

defaults to FALSE. If knifeedge is TRUE then the logistic values < the depend value of inL50 is set to zero, and all those >= inL50 are set to 1.0, approximating knife-edge selectivity

Value

A vector of length(depend) with the predicted logistic values

Examples

in50 <- 100.0
deltaS <- 8.0
lens <- seq(2,210,2)
select <- logist(inL50=in50,delta=deltaS,depend=lens)
selectk <- logist(in50,deltaS,lens,knifeedge=TRUE)
round(cbind(lens[35:70],select[35:70],selectk[35:70]),5)