Indefinite inner product space
（重定向自Krein space）
In mathematics, in the field of functional analysis, an indefinite inner product space
is an infinite-dimensional complex vector space ![K](/Images/godic/202501/22/a5f3c6a11b03839d46af9fb43c97c1881546.png")
equipped with both an indefinite inner product
and a positive semi-definite inner product
where the metric operator ![J](/Images/godic/202501/22/ff44570aca8241914870afbc310cdb851546.png")
is an endomorphism of obeying