.BG
.VE $Header: /usr3/s/current/s/.help/RCS/atan,v 1.2 83/12/30 19:24:22 rab Exp $
.FN atan
.TL
atan: Inverse Tangent
.CS
atan(a)
atan(a, b)
.PP
.AG a
numeric structure giving tangents of desired angles.
Missing values (NAs) are allowed.
.AG b
numeric structure which along with `a', determines the
tangent of the desired angle as `a/b'.  The two-argument
version should be used if `b' may be near zero.
Missing values (NAs) are allowed.
.RT
the angles in radians.  Where both `a' and `b' are zero, the value is NA.
The range of the value is `\-pi/2 <= atan(a) <= pi/2' and
`\-pi < atan(a,b) <= pi'.
.KW basic*
.KW trig
.KW math
.WR
