$$\frac{d^2y}{dx^2} = -\frac{(d - a)\,u\,(1 - u)}{b^2\,(1 + u)^3}$$
Arguments
- x
Numeric vector. Independent variable (typically log10-concentration).
- a
Numeric scalar. Lower asymptote (baseline response).
- b
Numeric scalar. Scale parameter (\(b > 0\)); controls steepness.
- c
Numeric scalar. Inflection-point location on the x-axis.
- d
Numeric scalar. Upper asymptote (saturation response).