logit2: Double Logistic Probability

In JVAdams/artiFISHal: A Pelagic Fish Community Simulator

Description

Probability distribution function of double logistic curve, with ascending and descending limbs allowing for parabolic-shaped probabilities.

Usage

logit2(x, x50a, slopea, x50b, slopeb)

Arguments

x	A numeric vector.
x50a	A numeric scalar, the quantile at which small values of x have a 50% probability, the first "location" parameter.
slopea	A numeric scalar, the slope at which the probability for small values of x increases, the first "scale" parameter.
x50b	A numeric scalar, the quantile at which large values of x have a 50% probability, the second "location" parameter.
slopeb	A numeric scalar, the slope at which the probability for large values of x decreases, the second "scale" parameter.

Details

The double logistic function mimics the single logistic function if either of the location parameters are set to the extremes, x50a = -Inf or x50a = Inf.

References

This function is based on a modification of MATLAB [link] code provided by Kresimir Williams, NOAA-AFSC afsc.noaa.gov, at the Great Lakes Acoustic Users Group's Workshop on Trawl Performance, hosted by the Great Lakes Fishery Commission glfc.org, 22-24 April 2014, in Ann Arbor, Michigan, USA.

Examples

x <- 1:400
y1 <- logit2(x=x, x50a=90, slopea=10, x50b=Inf, slopeb=-20)
plot(x, y1)

y2 <- logit2(x=x, x50a=-Inf, slopea=10, x50b=300, slopeb=-20)
plot(x, y2)

y3 <- logit2(x=x, x50a=90, slopea=10, x50b=300, slopeb=-20)
plot(x, y3)

JVAdams/artiFISHal documentation built on May 7, 2019, 10:14 a.m.