self start for Declining Logistic Function
Self starter for declining logistic function with parameters asym, a2, xmid and scal
dlf(time, asym, a2, xmid, scal) SSdlf(time, asym, a2, xmid, scal)
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 |
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).
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
## 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")
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