Table 2: properties of ILUFF1, ILUFF2, ILUFF3, and ILUFF4 preconditioners.

MethodILUFF1ILUFF2ILUFF3ILUFF4

Density 𝑃 timeDensity 𝑃 timeDensity 𝑃 timeDensity 𝑃 time

hor-131 0.984696 22.031 1.098996 43.86 0.990435 32.422 1.075562 32.64
sherman2 0.463237 466.531 0.682342 742.432 0.462847 637.203 0.687668 666.312
cavity05 0.272646 736.343 0.338992 1567.223 0.280553 1079.63 0.368013 1139.59
cavity060.291794 678.782 0.376243 1484.22 0.295636 993 0.407515 817.828
sherman4 1.243001 266.203 1.312467 804.922 1.243001 319.172 1.321447 574.328
epb01.575348 943.093 1.981968 2360.44 1.750386 1274.88 2.248583 1777.27
pde2961 1.234763 6996.83 1.327048 10863 1.248269 5879.3 1.334248 9262.47