= Parasitic amplification root
An amplification root of a <multistep method> is parasitic when it represents an additional numerical mode rather than the principal mode approximating the exact differential-equation flow. For a consistent method the principal root starts at one as the step tends to zero, while other roots can start elsewhere. A simple parasitic root on the unit circle is compatible with <zero-stability>, but its motion outside the circle for a negative test parameter can destroy <absolute stability>. Fixed-time convergence and all-time damping must be distinguished.
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