HP 3000 Manuals

Compiler Library/XL Reference Manual

ATAN (or ATAN') 

ATAN calculates the arctangent of a real number.

Declaration 

     FUNCTION ATAN(VAR x:REAL):REAL; EXTERNAL;

Accuracy 

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Attributes 

Parameter:                A real number.

Result:                   A representable real number in the range
                          [-pi/2,pi/2].  See Chapter 1 for details on the
                          internal representation of real numbers.

HP FORTRAN 77/XL:         Intrinsic function:  Y=ATAN(X).

Error:                    If the argument is a NaN, there are two cases.
                          If the INVALID trap is enabled, the message
                          "ATAN(X): X=NaN" occurs.  Otherwise, the
                          INVALID flag is set.  In either case, a quiet
                          NaN is returned.

Special Values 

                 atan (+Infinity) = pi/2

                 atan (-Infinity) = -pi/2

MPE/iX 5.0 Documentation