# What does ℜ symbol mean?

I came across the symbol $\mathfrak{R}$ in the Kalman introduction: Kalman Filter Intro

$$x\in \mathfrak{R}^m$$ It was used in this context:

$$x_{k} = Ax_{k–1} + Bu_{k – 1} + w_{k – 1}$$ What does $\mathfrak{R}$ stand for?

## migrated from mathematica.stackexchange.comJul 7 '16 at 9:54

This question came from our site for users of Wolfram Mathematica.

It means $x$ is an $m$-vector of real values. $\mathfrak{R}$ itself is the set of real numbers.
• I'd like to point out that nowadays $\mathbb{R}^m$ ("blackboard bold") is much more common. – Matt L. Jul 7 '16 at 11:10