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# tan(+Number, -Result)

Evaluates the trigonometric function tan(Number) and unifies the resulting value with Result.

Number
  A number.
Result
  Output: float or breal.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to tan(Number, Result) is equivalent to

        Result is tan(Number)

which should be preferred for portability.

In coroutining mode, if Number is uninstantiated, the call to tan/2 is delayed until this variable is instantiated.

### Modes and Determinism

- tan(+, -) is det

### Exceptions

(4) instantiation fault
  Number is not instantiated (non-coroutining mode only).
(24) number expected
  Number is not of a numeric type.
(20) arithmetic exception
  Illegal arithmetic operation: Number is (2k +1) * pi/2 for every integer k.

## Examples

    Success:
        Result is tan(0).		% gives Result = 0.0
        Result is tan(12.3).        % gives Result = -0.272854
        Result is tan(-1).          % gives Result = -1.55741

    Error:
        X is pi/2, tan(X). 		% arithmetic exception

## See Also

is / 2