

    \filetitle{difflog}{First log-difference pseudofunction}{modellang/difflog}

	\paragraph{Syntax}
 
 \begin{verbatim}
 difflog(EXPR)
 difflog(EXPR,K)
 \end{verbatim}
 \paragraph{Description}
 
 If the input argument \texttt{K} is not specified, this pseudofunction
 expands to
 
 \begin{verbatim}
 (log(EXPR)-log(EXPR{-1}))
 \end{verbatim}
 If the input argument \texttt{K} is specified, it expands to
 
 \begin{verbatim}
 (log(EXPR)-log(EXPR{K}))
 \end{verbatim}
 The two derived expressions, \texttt{EXPR\{-1\}} and \texttt{EXPR\{K\}},
 are based on \texttt{EXPR}, and have all its time subscripts shifted by
 ---1 or by \texttt{K} periods, respectively.
 
 \paragraph{Example}
 
 The following two lines of code
 
 \begin{verbatim}
 difflog(Z)
 difflog(X{1}/Y{-1},-2)
 \end{verbatim}
 will expand to
 
 \begin{verbatim}
 (log(Z)-log(Z{-1}))
 (log(X{1}/Y{-1})-log(X{-1}/Y{-3}))
 \end{verbatim}


