probit_spline2: quadratic spline specification model with probit link
Description
All specification models can be used as parameter in estimate.functional.
Specification models are used to denote the quantile or expectile level
(depending on the identifciation function).
This specification model depends through a quadratic spline on the state
variable and applies a probit link function.
# NOT RUN {# plot example of quadratic spline specification model with state-dependent quantile/expectile levelplot(function(x) probit_spline2(x,theta=c(0,1,-1)), xlim=c(-2,2))
# }