Richard Johnson, C.Anderson, B. D.O.2026-01-022026-01-020096-3518ORCID:/0000-0002-1493-4774/work/174739852https://hdl.handle.net/1885/733803034A perturbed error system is used to describe the parameter and output error behaviors of reduced-order application of adaptive identifier/filters such as the hyperstable adaptive recursive filter (HARF). Given satisfaction of a sufficient excitation condition, this error system is shown to exhibit a bounded-input, bounded-state (BIBS) property. This implies that, despite order insufficiency, the output and parameter estimates of HARF (and similar adaptive identifier/filter algorithms) remain bounded.4en198110.1109/TASSP.1981.11637010019659569