The first time for obtaining estimates for the transition probabilities, bivariate distribution function. NULL is equivalent to 0.
time2
The second time for obtaining estimates for the bivariate distribution function.
tp
Optional argument: tp="all" (default value) to obtain all the transition probabilities p11, p12 and p22; tp="p11" to obtain only p11; tp="p12" to obtain only p12;tp="p22" to obtain only p22.