Friedrichs Extension

In functional analysis, the Friedrichs extension is a canonical self-adjoint extension of a non-negative densely defined symmetric operator. It is named after the mathematician Kurt Friedrichs. This extension is particularly useful in situations where an operator may fail to be essentially self-adjoint or whose essential self-adjointness is difficult to show.

An operator T is non-negative if

Read more about Friedrichs Extension:  Examples, Definition of Friedrichs Extension, Krein's Theorem On Non-negative Self-adjoint Extensions

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