thanks for bringing this up. actually a 0 dimensional matrix because it fails to contain any values. it is an empty shell; a random tests byproduct for frustration purposes. would help to see this specific empty matrix in standard tests.

The error message is wrong, but the test is correct. build_one_two_three().next.next.next is None, and it has no data attribute.

I think I simply indicated a possibility for those (and there are) who don't want to calculate integrals.

I can't really spot the change :P Other than the fact that my code now times out. I guess you added more tests?

Edit: it's hard for me to believe how much faster this other method is...