---
title: Graph and Closedness
parent: Unbounded Operators
nav_order: 2
---

# {{ page.title }}

{% definition Graph of an Operator %}
The *graph* of an operator $T$ in a Hilbert space $\hilb{H}$
is the set of all pairs $(x,y) \in \hilb{H}\times\hilb{H}$
where $x$ lies in the domain of $T$ and $y=Tx$.
{% enddefinition %}