Hi, it just took me a while to realize that (inside mpi) I cannot write the following: ... string aggrop = "sum" mpireduce(&m, aggrop) ... but instead I need to go with string substitution: mpireduce(&m, @aggrop) I think the doc on p. 4 of the MPI guide is misleading there when it says string argument (for mpireduce, mpiallred, mpiscatter). It's rather a keyword apparently. I'm guessing that a string literal would work, but haven't tried. Slightly related about string representations: Consider a string inside a bundle: b = defbundle("a", "ohoh") print b # gives: a = ohoh The meaning is pretty clear of course, but both the single equal sign (instead of ":" or perhaps "==") and the non-quotation of this string literal looks strange to me given the gretl rules. thanks sven