Kristian Behrens, Cem Ertur, and Wilfried Koch, "'Dual' Gravity: Using 
Spatial Econometrics to Control for Multilateral Resistance", Journal of
Applied Econometrics, Vol. 27, No. 5, 2012, pp. 773-794.

The data are provided in two formats. The file data.txt is an ASCII file in
DOS format that is zipped in bek-data.zip. The file bek-data.xls is an Excel
file that is zipped in bek-data-excel.zip. Unix/Linux users should use
"unzip -a" on the former but must *not* use the "-a" option on the latter.

The variables in data.txt are described in estimgrav.m and in the Excel
file bek-data.xls.

Various Matlab .m files, all of which are ASCII files in DOS format, are
zipped in bek-programs.zip. Unix/Linux users should use "unzip -a".

In order to estimate the model, we use Matlab routines of James Lesage
found at: http://www.spatial-econometrics.com/.

In order to replicate our estimation, it is necessary to download their
routines and use the joint .m file: estimgrav.m

It is also necessary to keep all the .m files in the same directory.

The files sargrav.m and sacgrav.m include information matrices. sacgrav.m
corresponds to the sarar model in the paper. sarma.m and LVsarma.m allow
homogenous coefficients estimation of our model whereas sarmadouble.m and
LVsarmadouble.m allow heterogenous coefficients estimation of our model.