Function: _def_format
Class: default
Section: default
C-Name: sd_format
Prototype:
Help:
Doc: of the form x$.n$, where x (conversion style)
 is a letter in $\{\kbd{e},\kbd{f},\kbd{g}\}$, and $n$ (precision) is an
 integer; this affects the way real numbers are printed:

 \item If the conversion style is \kbd{e}, real numbers are printed in
 \idx{scientific format}, always with an explicit exponent,
 e.g.~\kbd{3.3 E-5}.

 \item In style \kbd{f}, real numbers are generally printed in
 \idx{fixed floating point format} without exponent, e.g.~\kbd{0.000033}. A
 large real number, whose integer part is not well defined (not enough
 significant digits), is printed in style~\kbd{e}. For instance
 \kbd{10.\pow 100} known to ten significant digits is always printed in style
 \kbd{e}.

 \item In style \kbd{g}, nonzero real numbers are printed in \kbd{f} format,
 except when their decimal exponent is $< -4$, in which case they are printed
 in \kbd{e} format. Real zeroes (of arbitrary exponent) are printed in \kbd{e}
 format.

 The precision $n$ is the number of significant digits printed for real
 numbers, except if $n<0$ where all the significant digits will be printed
 (initial default is 38 decimal digits). For more powerful formatting
 possibilities, see \tet{printf} and \tet{strprintf}.

 The default value is \kbd{"g.38"}.
