rational (Function) (ANSI and GNU Common Lisp Document)

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#### 12.2.54 rational, rationalize [Function]

`rational` number ⇒ rational

`rationalize` number ⇒ rational

#### Arguments and Values::

number—a real.

rational—a rational.

#### Description::

rational and rationalize convert

reals

to rationals.

If number is already rational, it is returned.

If number is a float, rational returns a rational that is mathematically equal in value to the float. rationalize returns a rational that approximates the float to the accuracy of the underlying floating-point representation.

rational assumes that the float is completely accurate.

rationalize assumes that the float is accurate only to the precision of the floating-point representation.

#### Examples::

     (rational 0) ⇒  0
     (rationalize -11/100) ⇒  -11/100
     (rational .1) ⇒  13421773/134217728 ;implementation-dependent
     (rationalize .1) ⇒  1/10

#### Affected By::

The implementation.

#### Exceptional Situations::

Should signal an error of type type-error if number is not a real. Might signal arithmetic-error.

#### Notes::

It is always the case that

     (float (rational x) x) ≡ x

and

     (float (rationalize x) x) ≡ x

That is, rationalizing a float by either method and then converting it back to a float of the same format produces the original number.