[Gretl-devel] seasonal cumulation?

Hi, it occurred to me that we have the diff/cum pair of functions, but for seasonal periodicities we only have sdiff, not "scum" (which maybe wouldn't be an ideal name anyway ;-) Maybe the cum() function could be extended with an optional argument that would allow to invoke a seasonal-step-style cumulation? For example, for quarterly data the result would be out(t) = in(t) + in(t-4), such that sdiff(out) would give you back 'in'. thanks sven