My question is really simple. I've already found a definition of $a^{1/2}=\sqrt{a}$, whenever $a$ is a positive real number. Are there other authors who define as $a^{1/2}=\pm\sqrt{a}$?
EDIT
My definition of $\sqrt a (a>0)$ is the standard one. The positive solution of the equation $x^2-a=0$.