

   CCrreeaattee oorr aadddd ttoo aa ttiimmee--vvaarryyiinngg ccoovvaarriiaattee ((ttvvccoovv)) oobbjjeecctt

        tvctomat(tvcov, names=NULL, index=NULL, tccov=NULL, oldtvcov=NULL)

   AArrgguummeennttss::

      tvcov: A list of matrices with time-varying covariate
             values for each individual (one column per vari-
             able), one matrix or dataframe of such covariate
             values (when there is only one such covariate), or
             an object of class, tvcov.

      names: The names of the time-varying covariates in tvcov
             (if the matrices do not have column names) or the
             name of the time-constant covariate.

      index: The index numbers or names of variables in tvcov,
             with that class, for which an interaction is to be
             added or one such number or name for an interac-
             tion with a time-constant covariate.

   oldtvcov: An object of class, tvcov, to which tvcov is to be
             added.

   DDeessccrriippttiioonn::

        `tvctovmat' transforms a list of matrices with time-
        varying covariates for each individual or one matrix or
        dataframe of such covariate values into an object of
        class, tvcov, or combines two such objects. It can also
        add interactions among covariates.

        Such objects can be printed. Methods are available for
        extracting the covariates and their names.

   VVaalluuee::

        Returns an object of class, tvcov, containing a matrix
        for the covariates (z$tvcov) with one row per response
        per individual and a vector giving the number of obser-
        vations per individual (z$nobs).

   AAuutthhoorr((ss))::

        J.K. Lindsey

   SSeeee AAllssoo::

        `gettvc', `read.list', `restovec', `rmna', `tcctomat'.

   EExxaammpplleess::

        z <- matrix(rpois(20,5),ncol=5)
        tvctomat(z)

