nlraa (version 0.53)

SSdlf: self start for Declining Logistic Function

Description

Self starter for declining logistic function with parameters asym, a2, xmid and scal

Usage

dlf(time, asym, a2, xmid, scal)
SSdlf(time, asym, a2, xmid, scal)

Arguments

time

input vector (x) which is normally ‘time’, the smalles value should be close to zero.

asym

value of weight or mass at its peak (maximum)

a2

value of weight or mass at its trough (minimum)

xmid

time at which half of the maximum weight or mass has bean reached.

scal

scale parameter which controls the spread also interpreted in terms of time to go from xmid to approx. 0.63 asym

Value

a numeric vector of the same length as x (time) containing parameter estimates for equation specified

dlf: vector of the same length as x (time) using the declining logistic function

Details

Response function: $$y = (asym - a2) / (1 + exp((xmid - time)/scal))) + a2$$.

• asym: upper asymptote

• xmid: time when y is midway between w and a

• scal: controls the spread

• a2: lower asymptote

The four parameter logistic SSfpl is essentially equivalent to this function, but here the interpretation of the parameters is different and this is the form used in Oddi et. al. (2019) (see vignette).

Examples

# NOT RUN {
## Extended example in the vignette 'nlraa-Oddi-LFMC'
x <- seq(0, 17, by = 0.25)
y <- dlf(x, 2, 10, 8, 1)
plot(x, y, type = "l")
# }