ToC DocOverview CGDoc RelNotes Index PermutedIndex
Allegro CL
Home Previous Up Next Table of Contents Index
  ANSI Common Lisp   12 Numbers   12.2 Dictionary of Numbers

12.2.38 sqrt, isqrt Function

Syntax:
sqrt number    root

isqrt natural    natural-root

Arguments and Values:
number, root - a number.

natural, natural-root - a non-negative integer.

Description:
sqrt and isqrt compute square roots.

sqrt returns the principal square root of number. If the number is not a complex but is negative, then the result is a complex.

isqrt returns the greatest integer less than or equal to the exact positive square root of natural.

If number is a positive rational, it is implementation-dependent whether root is a rational or a float. If number is a negative rational, it is implementation-dependent whether root is a complex rational or a complex float.

The mathematical definition of complex square root (whether or not minus zero is supported) follows:

(sqrt x) = (exp (/ (log x) 2))

The branch cut for square root lies along the negative real axis, continuous with quadrant II. The range consists of the right half-plane, including the non-negative imaginary axis and excluding the negative imaginary axis.

Examples:
 (sqrt 9.0)  3.0
 (sqrt -9.0)  #C(0.0 3.0)
 (isqrt 9)  3
 (sqrt 12)  3.4641016
 (isqrt 12)  3
 (isqrt 300)  17
 (isqrt 325)  18
 (sqrt 25)
 5
OR5.0
 (isqrt 25)  5
 (sqrt -1)  #C(0.0 1.0)
 (sqrt #c(0 2))  #C(1.0 1.0)

Exceptional Situations:
The function sqrt should signal type-error if its argument is not a number.

The function isqrt should signal type-error if its argument is not a non-negative integer.

The functions sqrt and isqrt might signal arithmetic-error.

See Also:
exp, log, Section 12.1.3.3 Rule of Float Substitutability

Notes:
 (isqrt x) ==(values (floor (sqrt x))) 
but it is potentially more efficient.

Allegro CL Implementation Details:
None.

Home Previous Up Next Table of Contents Index
© Franz Inc. 1998-2017 - File last updated 01-11-2017