Figure 4From: Preconditioners for reduced saddle point systems arising in elliptic PDE-constrained optimization problems The eigenvalue distribution of the preconditioned matrix \(\pmb{P_{\mathrm{btd}}^{-1}\mathcal{A}}\) with \(\pmb{\beta=10^{-8}}\) and \(\pmb{h=2^{-3}}\) . Back to article page