Symbols:R

The Set of Real Numbers
$$\R$$

The set of real numbers.

Its LaTeX code is \mathbb{R}, \reals or \R.

Some authors use $$R$$.

The Set of Non-Zero Real Numbers
$$\R^*$$

The set of non-zero real numbers:
 * $$\R^* = \R - \left\{{0}\right\}$$.

Its LaTeX code is \mathbb{R}^*, \reals^* or \R^*.

The Set of Non-Negative Real Numbers
$$\R_+$$

The set of non-negative real numbers:
 * $$\R_+ = \left\{{x \in \R: x \ge 0}\right\}$$.

Its LaTeX code is \mathbb{R}_+, \reals_+ or \R_+</tt>.

The Set of Strictly Positive Real Numbers
$$\R_+^*$$

The set of strictly positive real numbers:
 * $$\R_+^* = \left\{{x \in \R: x > 0}\right\}$$.

Its LaTeX code is \mathbb{R}_+^*</tt>, \reals_+^*</tt> or \R_+^*</tt>.