[Gretl-users] Re: object could not rebuilt

This is by way of response to Dimitris Brilakis, who reported recently that when he saved nonlinear least squares models into a gretl session file, these models could not be rebuilt when the session file was reopened. This is now fixed in gretl's git repository and the current snapshots at sourceforge. Fixed, that is, in the sense that current gretl will not produce session files that have this problem. Unfortunately, this does not mean that gretl will now successfully read "old" session files that have the problem in question. However, such session files can be fixed, and if anyone has a bad session file that is valuable to them, send it to me and I can fix it. I'm adding an account of the details below in case anyone is interested. A gretl session file is a zipped collection of XML files. When writing strings into an XML file one has to be careful with strings that might contain the bytes '<' or '>' since these are special in XML, indicating the start or end of a "tag". These bytes have to be "escaped", substituting "&lt;" for '<' and "&gt;" for '>'. We've been doing that in most cases, but we missed the "depvar" element in a gretl model. For most models, "depvar" is just the name of a series (the dependent variable) and that can never contain XML-special characters. But in the case of NLS the "depvar" string is the formula that specifies the nonlinear regression function, and that may contain problematic characters. So now we ensure that the depvar string is properly escaped, if needed, when saving a session file. How to fix an old session file? You have to unzip the .gretl file, find the model files, open them in a text editor, and within the "depvar" string replace any instances of '<' with "&lt;" and any instances of '>' with "&gt;". Then zip the file up again and it should be OK. Some gretl users may be OK with doing this themselves, but as mentioned above I'm willing to perform the fix if needed. Allin Cottrell