Nightmare Matrices 2: Symmetric Positive Definite Case

I present here a deliberately unpleasant family for sparse linear solvers that operate only on an input sparse matrix. This counter-example is closely related to the nightmare matrices of a previous post , but with a key strengthening: the matrices I present here will be symmetric and positive definite (“SPD” for short). In my prior post I relied on indefiniteness of the matrix to make iterative…