So this seems like a path problem. I believe the solution is to change the path in the Makevars file, but I have no idea how to do that. I would appreciate step-by-step instructions on that solution, or suggestions on other possible solutions.
If you’ve already gone through those instructions (like the steps for checking BINPREF) and it still isn’t working then hopefully one of my Windows literate colleagues like @andrjohns or @bgoodri will be able to help you get this fixed.
TRANSLATING MODEL 'schools' FROM Stan CODE TO C++ CODE NOW.
successful in parsing the Stan model 'schools'.
'C:/rtools40/usr/mingw_/bin/g++' not found
CHECKING DATA AND PREPROCESSING FOR MODEL 'schools' NOW.
Error in data_list2array(x) :
the dimensions for all elements (array) of the list are not same
failed to preprocess the data; sampling not done
That worked! As for my ulam code, now I think the problem was just that it takes an extremely long to run, so I was giving up on it assuming it was stuck and that the warning message was telling me the reason.