Wikipedia:Articles for deletion/Adjoint filter
Multiple RS in the article and in a GScholar search show this concept exists in the signal processing and control theory literature. There is enough sourcing for a reasonable stub. Merging to Hermitian adjoint would also be fine. But deletion of verifiable content should be avoided per 
— User:Mark, 11:21, 4 September 2017 (UTC)
Stance: keep
Cited policy: WP:ATD (Wikipedia:Deletion policy)