Compiler Library/XL Reference Manual (32650-90029)

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argument is zero) there are two possible

actions. If the INVALID trap is enabled, the

message "AMOD(X,Y): ANY OF X AND Y=NaN OR

X=INFINITY OR Y=0.0" occurs. Otherwise, the

INVALID flag is set. In either case, a quiet

NaN is returned.

ATAN (or ATAN')

ATAN calculates the arctangent of a real number.

Declaration

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

Accuracy

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

ATAN2 (or ATAN2')

ATAN2 calculates the arctangent of the quotient of two real numbers.

Declaration

FUNCTION ATAN2(VAR x,y:REAL):REAL; EXTERNAL;

Accuracy

When x-y ~ ∈ , maximum f-g ~ ∈

1 + x

When x-y ~ ∈ , maximum f-g ~ ∈

1 + w