On Mon, 4 Mar 2013, Pindar wrote: That's because there's a difference between an empty matrix and a null matrix. In fact, isnull() is typically used to check for optional matrix arguments in functions. See the following script snippet: <hansl> function void boo(matrix *a[null]) if isnull(a) printf "Ha!\n" else printf "Nope\n" endif end function function scalar isempty(matrix a) return (rows(a) == 0 || cols(a) == 0) end function matrix test = {1,0,3;1,1,100} boo(&test) boo() matrix seek = selifr(seek,seek[,2].=2) eval seek eval isempty(seek) </hansl> ------------------------------------------------------- Riccardo (Jack) Lucchetti Dipartimento di Scienze Economiche e Sociali (DiSES) Università Politecnica delle Marche (formerly known as Università di Ancona) r.lucchetti(a)univpm.it http://www2.econ.univpm.it/servizi/hpp/lucchetti -------------------------------------------------------

On Mon, 4 Mar 2013, Pindar wrote: (where the matrix in question exists but has zero rows and columns). As the help for isnull() states, this function "Returns 0 if name is the identifier for a currently defined object, be it a scalar, a series, a matrix, list, string or bundle; otherwise returns 1." So it correctly returns 1 for an empty (0 x 0) matrix. However, there is admittedly something confusing here in that if you do matrix m = zeros(0,0) print m then gretl comes back with "m: matrix is null (0 x 0)". I've now changed that message in CVS to say "matrix is empty". (One could defend the distinction between a null matrix and a null (non-existent) object, but I won't go there.) You also state that the ok() function is not working for matrices, as in (trimming a little), Well, ok(test) is fine: it produces a 2 x 3 matrix of 1s, as per the help -- since "test" contains no non-finite elements. However the result from ok(seek) is arguably wrong: this gives a "Data error" (the matrix in question being empty), while according to the help text it probably should return an empty matrix. This would be consistent with the recent "upgrading" of empty matrices in general (that is, we try to treat them simply as special cases rather than as invalid objects, to the extent possible and reasonable). Allin Cottrell