What does |x| mean in the erf function?

[moonman239]

Here's the equation I'm using: erf(x) = x/|x| * SQRT(1 - exp(-x2*(4/pi + (ax)2) / (1 + ax2)

[awkward]

Here's the equation I'm using: erf(x) = x/|x| * SQRT(1 - exp(-x2*(4/pi + (ax)2) / (1 + ax2)

|x| is the absolute value of x.

x/|x| is 1 for positive x, -1 for negative x.

(However, I don't recognize that equation for erf.)