HYPOT(3M) HYPOT(3M)
NAME
hypot, cabs - Euclidean distance, complex absolute value
SYNOPSIS
#include <math.h>
double hypot(x,y)
double x,y;
double cabs(z)
struct {double x,y;} z;
DESCRIPTION
Hypot(x,y) and cabs(x,y) return sqrt(x*x+y*y) computed in such a way that underflow will not happen, and overflow occurs only if the final
result deserves it.
hypot(infinity,v) = hypot(v,infinity) = +infinity for all v, including NaN.
ERROR (due to Roundoff, etc.)
Below 0.97 ulps. Consequently hypot(5.0,12.0) = 13.0 exactly; in general, hypot and cabs return an integer whenever an integer might be
expected.
The same cannot be said for the shorter and faster version of hypot and cabs that is provided in the comments in cabs.c; its error can
exceed 1.2 ulps.
NOTES
As might be expected, hypot(v,NaN) and hypot(NaN,v) are NaN for all finite v; with "reserved operand" in place of "NaN", the same is true
on a VAX. But programmers on machines other than a VAX (it has no infinity) might be surprised at first to discover that hypot(+-infin-
ity,NaN) = +infinity. This is intentional; it happens because hypot(infinity,v) = +infinity for all v, finite or infinite. Hence
hypot(infinity,v) is independent of v. Unlike the reserved operand on a VAX, the IEEE NaN is designed to disappear when it turns out to be
irrelevant, as it does in hypot(infinity,NaN).
SEE ALSO
math(3M), sqrt(3M)
AUTHOR
W. Kahan
4th Berkeley Distribution May 12, 1986 HYPOT(3M)