Create asymmetric unit around structure

[RachelAlcraft]

In order to make the thevenaz beta spline method work as periodic with boundary conditions rather than mirror one option is to belnd the coefficient matrix:

It is trivial to get out coefficients from beyonf the bvoundaries periodically but the calculaiton of the coefficients themselves calculaiton is more confusing. This method is effectively a workaround rather than a solution.

[RachelAlcraft]

This might be a better diagram - in 3d there would be 8