[ Arithmetic | The ECLiPSe Built-In Predicates | Reference Manual | Alphabetic Index ]

atan(+Number, ?Result)

Evaluates the trigonometric function atan(Number) and unifies the resulting value with Result.
+Number
A number.
?Result
A variable, float or breal.

Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to atan(Number, Result) is equivalent to 
    Result is atan(Number)
which should be preferred for portability.

In coroutining mode, if Number is a free variable, the call to atan/2 is delayed until this variable is instantiated.

Fail Conditions

Fails if the result of the evaluation does not unify with Result.

Resatisfiable

No

Exceptions

(4) instantiation fault
Number is not instantiated (non-coroutining mode only).
(5) type error
Result is a number but not a float or breal
(24) number expected
Number is not of a numeric type.
(24) number expected
Result is neither a number nor a variable.

Examples

Success:
      atan(0.0, 0.0).
      atan(1.0, Result).       (gives Result = 0.785398)
      atan(-8, Result).        (gives Result = -1.44644)
Fail:
      atan(1, 0.0).
Error:
      atan(A, 6.0).                   (Error 4).
      atan(1.55741, 1).               (Error 5).
      atan(1 + 0.55741, 1.0).         (Error 24).
      atan(5, r).                     (Error 24).

See Also

is / 2