verified to pass 2025/2026
proper nodal source - correct answer ✔repeated, positive, real with 2 LI EV
proper nodal sink - correct answer ✔repeated, negative, real with 2 LI EV
improper nodal source - correct answer ✔distinct positive real OR repeated positive real without 2 LI
EV
improper nodal sink - correct answer ✔distinct negative real OR repeated negative real without 2 LI EV
saddle point - correct answer ✔real, opposite signs
center - correct answer ✔purely imaginary
spiral source - correct answer ✔positive real part of imaginary
spiral sink - correct answer ✔negative real part of imaginary
parallel lines - correct answer ✔0 and a negative real OR repeated 0 without 2 LI EV