Effcient Estimation of a SemiparametricTime-Varying Coeffcient Model for Interval-Censored Failure Time Data

density is the loglikelihood function.

densitygrad is the derivative of the loglikelihood function.

spdensity is the loglikelihood function after parameterization by B-Splines.

spdensitygrad is the derivative of the loglikelihood function after parameterization by B-Splines.

defaultknots is the function to determine knots sequences of B-Splines given samples.

fit is the fit function and return the estimation results.