Inverse of the 4PL Model

Solves analytically for x: $$x = c + b\,\log\!\frac{y - a}{d - y}$$

Usage

inv_logistic4(y, a, b, c, d, tol = 1e-06)

inv_logistic4_fixed(y, fixed_a, b, c, d)

Arguments

y

Numeric vector. Observed response values.

a, b, c, d

Numeric scalars. Model parameters.

tol

Numeric scalar. Buffer from asymptotes. Default 1e-6.

fixed_a

Numeric scalar. Externally fixed lower asymptote.

Value

Numeric vector of x values. NA for out-of-range y.

See also

Other inverse-functions: inv_gompertz4(), inv_logistic5(), inv_loglogistic4(), inv_loglogistic5()