Here's a belated response to Sven's question in http://lists.wfu.edu/pipermail/gretl-devel/2015-February/005544.html To reprise his question: suppose we have matrices a and b as follows: a (3 x 2) 1 1 1 1 1 1 b (1 x 3) 0 1 2 Now we do c = a ~ b, and gretl gives us c (3 x 3) 1 1 0 1 1 0 1 1 0 Is this a bug or a feature? I think it's a bug: this should provoke an error. I believe the code in question (gretl_matrix_col_concat(), in gretl_matrix.c) reflects the intent that if b were a 1 x 1 matrix we would append to a column that repeats b's single element -- as an acceptable generalization of columnwise concatenation -- but it fails to determine whether b really is 1 x 1. Jack, do you think that's right? If so I'll go ahead and fix it. Allin