mature {MQMF}

mature alternative logistic function commonly used for maturity

Description

mature a function 1/(1+(1/exp(a + b x sizeage))) which can be expressed as exp(a + b x sizeage)/(1 + exp(a + b x sizeage)). This describes a symmetric logistic curve that has the property Lm50 = -a/b and the inter-quartile distance is 2.log(3)/b.

Usage

mature(a, b, sizeage)

Arguments

a

is the intercept of the exponential function usually -ve

b

is the gradient of the exponential function

sizeage

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

Value

A vector of predicted proportion mature for the sizeage

Examples

a <- -14.383
b <- 0.146017
lens <- seq(2,210,2)
round(mature(a,b,sizeage=lens),5) # length based
round(mature(-2.5,0.95,0:25),5)   # age based