Dear Alex,
You're right! Thanks for spotting this.
I think what has happened is that TOPAS has got a bit more rigorous about how it checks equations since that tutorial was written. The INP file online has the various parameters needed to describe the distortion mode amplitudes and xyz coordinates in the "for strs 1 to 1" section. That sits inside the "for xdds" section. What then happens is that the parameters get defined once for the X-ray pattern and once for the neutron. When the tutorial was written this didn't matter, but I guess it now does.
One solution is to take the sections of the inp file labelled '{{{ mode definitions '{{{mode-amplitude to delta transformation and '{{{distorted parameters, and move them further up the INP file (e.g. put them after the '{{{ control information section.
I haven't gone on to try the whole tutorial, so the fix might cause problems later on. I'll try and check over the next few days and update the tutorial accordingly. I'll email you a working INP file.
Thanks again.
John
P.S. tutorial now updated