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### `eval`, `deval`

`eval(obj[,prec])`
`deval(obj)`
  :: Evaluate obj numerically.

return
  number or expression
obj
  general expression
prec
  integer

- Evaluates the value of the functions contained in obj as far as possible.
- `deval` returns double float. Rational numbers remain unchanged in results from `eval`.
- In `eval` the computation is done by PARI. (See section `pari`.) In `deval` the computation is done by the C math library.
- `deval` cannot handle complex numbers.
- When prec is specified, computation will be performed with a precision of about prec-digits. If prec is not specified, computation is performed with the precision set currently. (See section `setprec`.)
- Currently available numerical functions are listed below. Note they are only a small part of whole PARI functions.
  `sin`, `cos`, `tan`, `asin`, `acos`, `atan`, `sinh`, `cosh`, `tanh`, `asinh`, `acosh`, `atanh`, `exp`, `log`, `pow(a,b) (a^b)`
- Symbols for special values are as the followings. Note that `@i` cannot be handled by `deval`.
  `@i`
    unit of imaginary number
  `@pi`
    the number pi, the ratio of circumference to diameter
  `@e`
    Napier's number (`exp`(1))

    [118] eval(exp(@pi*@i));
    -1.0000000000000000000000000000
    [119] eval(2^(1/2));
    1.414213562373095048763788073031
    [120] eval(sin(@pi/3));
    0.86602540378443864674620506632
    [121] eval(sin(@pi/3)-3^(1/2)/2,50);
    -2.78791084448179148471 E-58
    [122] eval(1/2);
    1/2
    [123] deval(sin(1)^2+cos(1)^2);
    1

`References`
  section `ctrl`, section `setprec`, section `pari`.

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