On Mon, 20 Aug 2012, Logan Kelly wrote: > It strikes me that exp(cum(ln(index))) could be more costly both in > terms of cycles and added round-off error (though for the simple stuff I > do both are probably trivial). My concern with exp(cum(ln(index))) is > that it will not work if the series contains negative values?
Of course not, but: 1) does it make sense at all to compute the cumulative product of something that may be non-positive? Can you provide any real-world example? 2) the definitive solution was Allin's: y = y *y(-1) all the rest are just musings on the subject. -------------------------------------------------- Riccardo (Jack) Lucchetti Dipartimento di Economia Università Politecnica delle Marche (formerly known as Università di Ancona) r.lucchetti(a)univpm.it http://www2.econ.univpm.it/servizi/hpp/lucchetti --------------------------------------------------
