Function: Ser
Section: conversions
C-Name: gtoser
Prototype: GDnDP
Help: Ser(s,{v=x},{d=seriesprecision}): convert s into a power series with
 variable v and precision d, starting with the constant coefficient.
Doc: transforms the object $s$ into a power series with main variable $v$
 ($x$ by default) and precision (number of significant terms) equal to
 $d$ (= the default \kbd{seriesprecision} by default). If $s$ is a
 scalar, this gives a constant power series with precision \kbd{d}. If $s$
 is a polynomial, the precision is the maximum of \kbd{d} and the degree of
 the polynomial. If $s$ is a vector, the
 coefficients of the vector are understood to be the coefficients of the power
 series starting from the constant term (as in \tet{Polrev}$(x)$), and the
 precision $d$ is ignored.
 \bprog
 ? Ser(x^2,, 5)
 %1 = x^2 + O(x^7)
 ? Ser([1,2,3], t)
 %2 = 1 + 2*t + 3*t^2 + O(t^3)
 @eprog\noindent
 The warning given for \kbd{Pol} also applies here: this is not a substitution
 function.
