= Nonnegative real number
{title2=$\mathbb R_{\ge0}$}
A nonnegative real number is a <real number> $x\ge0$. The set of all such numbers is $\mathbb R_{\ge0}=[0,\infty)$, which includes zero as well as the positive real numbers. The word nonnegative is therefore weaker than strictly positive.
This set is closed under addition and multiplication, but negating a nonzero member leaves it. Every real square and every <absolute value> is nonnegative. A <variance> can equal zero, as it does for a constant <random variable>; calling every variance positive would incorrectly exclude that legitimate case. Nonnegative constraints similarly allow zero as a feasible boundary value in <mathematical optimization>.
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