[LISPWORKS][Common Lisp HyperSpec (TM)] [Previous][Up][Next]



rational number => rational

rationalize number => rational

Arguments and Values:

number---a real.

rational---a rational.


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.


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

Side Effects: None.

Affected By:

The implementation.

Exceptional Situations:

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

See Also: None.


It is always the case that

 (float (rational x) x) ==  x

 (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.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

[Starting Points][Contents][Index][Symbols][Glossary][Issues]
Copyright 1996-2005, LispWorks Ltd. All rights reserved.