Function: atan

atan is a function defined in floatfns.c.

Signature

(atan Y &optional X)

Documentation

Return the inverse tangent of the arguments.

If only one argument Y is given, return the inverse tangent of Y. If two arguments Y and X are given, return the inverse tangent of Y divided by X, i.e. the angle in radians between the vector (X, Y) and the x-axis.

Other relevant functions are documented in the number group.

View in manual

Probably introduced at or before Emacs version 22.1.

Shortdoc

;; number
(atan float-pi)
    => 1.2626272556789118

Source Code

// Defined in /usr/src/emacs/src/floatfns.c
{
  double d = extract_float (y);

  if (NILP (x))
    d = atan (d);
  else
    {
      double d2 = extract_float (x);
      d = atan2 (d, d2);
    }
  return make_float (d);
}