$$\frac{d^2y}{dx^2} = b^2\,(d - a)\,v\,(v - 1)\,\exp(-v) \quad\text{where } v = \exp(-b(x - c))$$
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).