num::refactor_block_cholesky_suffix

Defined in header <linear/factorization/block_tridiagonal.hpp>

block_cholesky_factor
refactor_block_cholesky_suffix(const spmat &A, view<const idx> levels,
                               const block_cholesky_factor &previous,
                               idx first_changed_block);

Reuse a block-Cholesky prefix and refactor only the changed suffix.

The retained diagonal factors are 0,...,j-1, and the retained scaled lower blocks are 0,...,j-2, where j = first_changed_block. The boundary coupling j-1 is recomputed because it touches the changed suffix.