IKbandwidth calculates the Imbens-Kalyanaraman optimal bandwidth
for local linear regression in Regression discontinuity designs.
IKbandwidth(X, Y, cutpoint = NULL, verbose = FALSE, kernel = "triangular")FALSE."triangular" (default and recommended),
"rectangular", "epanechnikov", "quartic", "triweight", "tricube",
"gaussian", and "cosine".