Compiler Library/XL Reference Manual (32650-90029)

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Attributes
Parameter: A longreal number.
Result: A representable longreal number in the range
[-pi/2, pi/2]. See Chapter 1 for details on
the internal representation of longreal
numbers.
HP FORTRAN 77/XL: Intrinsic function: Y=DATAN(X).
Error: If the argument is a NaN, there are two cases.
If the INVALID trap is enabled, the message
"DATAN(X): X=NaN" occurs. Otherwise, the
INVALID flag is set. In either case, a quiet
NaN is returned.
Special Values
datan (+Infinity) = pi/2
datan (-Infinity) = -pi/2
DATAN2
DATAN2 calculates the arctangent of the quotient of two longreal numbers.
Declaration
FUNCTION DATAN2(VAR x,y:LONGREAL):LONGREAL; EXTERNAL;
Accuracy
Attributes
Parameters: Longreal numbers; both must not be zero.
Result: A representable longreal number in one of the
following ranges: