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cl:functions:abs [2019/06/15 02:00] |
cl:functions:abs [2019/11/19 12:00] (current) |
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+ | ====== Function ABS ====== | ||

+ | |||

+ | ====Syntax==== | ||

+ | * **abs** //number// → //absolute-value// | ||

+ | |||

+ | ====Arguments and Values==== | ||

+ | * //number// - a //[[CL:Glossary:number]]//. | ||

+ | * //absolute-value// - a non-negative //[[CL:Glossary:real]]//. | ||

+ | |||

+ | ====Description==== | ||

+ | **abs** returns the absolute value of //number//. | ||

+ | |||

+ | If //number// is a //[[CL:Glossary:real]]//, the result is of the same //[[CL:Glossary:type]]// as //number//. | ||

+ | |||

+ | If //number// is a //[[CL:Glossary:complex]]//, the result is a positive //[[CL:Glossary:real]]// with the same magnitude as //number//. The result can be a //[[CL:Glossary:float]]// even if //number//'s components are //[[CL:Glossary:rationals]]// and an exact rational result would have been possible. | ||

+ | |||

+ | Thus the result of ''(abs #c(3 4))'' can be either ''5'' or ''5.0'', depending on the implementation. | ||

+ | |||

+ | ====Examples==== | ||

+ | <blockquote> | ||

+ | (abs 0) <r>0 </r> | ||

+ | (abs 12/13) <r>12/13 </r> | ||

+ | (abs -1.09) <r>1.09 </r> | ||

+ | (abs #c(5.0 -5.0)) <r>7.071068 </r> | ||

+ | (abs #c(5 5)) <r>7.071068 </r> | ||

+ | (abs #c(3/5 4/5)) <r>1 ; or approximately 1.0 </r> | ||

+ | ([[CL:Functions:eql]] (abs -0.0) -0.0) <r>//[[CL:Glossary:true]]//</r> | ||

+ | </blockquote> | ||

+ | |||

+ | ====Affected By==== | ||

+ | None. | ||

+ | |||

+ | ====Exceptional Situations==== | ||

+ | None. | ||

+ | |||

+ | ====See Also==== | ||

+ | * {\secref\FloatSubstitutability} | ||

+ | |||

+ | ====Notes==== | ||

+ | If //number// is a //[[CL:Glossary:complex]]//, the result is equivalent to the following: | ||

+ | |||

+ | <blockquote> | ||

+ | (abs //number//) ≡ ([[CL:Functions:sqrt]] ([[CL:Functions:math-add|+]] ([[CL:Functions:expt]] ([[CL:Functions:realpart]] //number//) 2) ([[CL:Functions:expt]] ([[CL:Functions:imagpart]] //number//) 2))) | ||

+ | </blockquote> | ||

+ | |||

+ | An implementation should not use this formula directly for all //[[CL:Glossary:complexes]]// but should handle very large or very small components specially to avoid intermediate overflow or underflow. | ||

+ | |||

+ | \issue{REAL-NUMBER-TYPE:X3J13-MAR-89} \issue{REAL-NUMBER-TYPE:X3J13-MAR-89} \issue{COMPLEX-RATIONAL-RESULT:EXTEND} | ||