num::refactor_block_lu_suffix

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

block_lu_factor refactor_block_lu_suffix(const spmat &A, view<const idx> levels,
                                         const block_lu_factor &previous,
                                         idx first_changed_block, real scale = 1.0);

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

Blocks before first_changed_block must be numerically unchanged from the matrix represented by previous. The coupling immediately before the changed block is assembled and eliminated again, because it touches the changed suffix. Thus a change beginning at block j retains diagonal factors 0,...,j-1 and scaled lower blocks 0,...,j-2.

The layout of the retained prefix is checked, while equality of its matrix entries is the caller's responsibility.