Functions and CALL Routines 
Returns the arc tangent.

argument

specifies a numeric constant, variable,
or expression.
The ATAN function returns the 2quadrant
arc tangent (inverse tangent) of the argument. The value that is returned
is the angle (in radians) whose tangent is x
and whose value ranges from 
to
. If the argument is missing, then ATAN returns a missing
value.
The ATAN function is similar to the ATAN2
function except that ATAN2 calculates the arc tangent of the angle from the
ratio of two arguments rather than from one argument.
SAS Statements 
Results 
x=atan(0);

0

x=atan(1);

0.7853981634

x=atan(9.0);

1.460139106

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