diff options
Diffstat (limited to 'manual/arith.texi')
| -rw-r--r-- | manual/arith.texi | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/manual/arith.texi b/manual/arith.texi index 7f8c205ebb..2e418838db 100644 --- a/manual/arith.texi +++ b/manual/arith.texi @@ -414,13 +414,19 @@ This function returns the absolute value of the floating-point number @deftypefunx float cabsf (complex float @var{z}) @deftypefunx {long double} cabsl (complex long double @var{z}) These functions return the absolute value of the complex number @var{z}. -The compiler must support complex numbers to use these functions. (See -also the function @code{hypot} in @ref{Exponents and Logarithms}.) The +The compiler must support complex numbers to use these functions. The value is: @smallexample sqrt (creal (@var{z}) * creal (@var{z}) + cimag (@var{z}) * cimag (@var{z})) @end smallexample + +This function should always be used instead of the direct formula since +using the simple straight-forward method can mean to loose accuracy. If +one of the squared values is neglectable in size compared to the other +value the result should be the same as the larger value. But squaring +the value and afterwards using the square root function leads to +unaccuracy. See @code{hypot} in @xref{Exponents and Logarithms}. @end deftypefun @node Normalization Functions |