\( \newcommand\al{\alpha} \newcommand\be{\beta} \newcommand\de{\delta} \newcommand\De{\Delta} \newcommand\eps{\epsilon} \newcommand\ga{\gamma} \newcommand\Ga{\Gamma} \newcommand\ka{\kappa} \newcommand\la{\lambda} \newcommand\La{\Lambda} \newcommand\om{\omega} \newcommand\Om{\Omega} \newcommand\sg{\sigma} \newcommand\Sg{\Sigma} \renewcommand\th{\theta} %--- Latex uses \th for a Norse character \newcommand\Th{\Theta} \newcommand\vphi{\varphi} % % some calligraphy % \newcommand\cA{{\mathcal A}} \newcommand\cB{{\mathcal B}} \newcommand\cC{{\mathcal C}} \newcommand\cD{{\mathcal D}} \newcommand\cE{{\mathcal E}} \newcommand\cF{{\mathcal F}} \newcommand\cG{{\mathcal G}} \newcommand\cH{{\mathcal H}} \newcommand\cI{{\mathcal I}} \newcommand\cJ{{\mathcal J}} \newcommand\cK{{\mathcal K}} \newcommand\cL{{\mathcal L}} \newcommand\cM{{\mathcal M}} \newcommand\cN{{\mathcal N}} \newcommand\cO{{\mathcal O}} \newcommand\cP{{\mathcal P}} \newcommand\cQ{{\mathcal Q}} \newcommand\cR{{\mathcal R}} \newcommand\cS{{\mathcal S}} \newcommand\cT{{\mathcal T}} \newcommand\cU{{\mathcal U}} \newcommand\cV{{\mathcal V}} % % fields and rings (and a semigroup) % \newcommand\cx{{\mathbb C}}% complexes \newcommand\fld{{\mathbb F}} \newcommand\flde{{\mathbb E}} \newcommand\ints{{\mathbb Z}} \newcommand\nn{{\mathbb N}}%non-negative integers \newcommand\re{{\mathbb R}}%reals \newcommand\rats{{\mathbb Q}} % % the really useful stuff % \newcommand\comp[1]{{\mkern2mu\overline{\mkern-2mu#1}}} \newcommand\diff{\mathbin{\mkern-1.5mu\setminus\mkern-1.5mu}}% for \setminus \newcommand\res{\mathbin{\mkern-2.0mu\restriction\mkern-2.0mu}} \newcommand\sbs{\subseteq} \newcommand\sps{\supseteq} \newcommand\seq[3]{#1_{#2},\ldots,#1_{#3}} \DeclareMathOperator{\supp}{supp} \DeclareMathOperator{\im}{im} \DeclareMathOperator{\row}{row} \newcommand\pmat[1]{\begin{pmatrix} #1 \end{pmatrix}} \newcommand\cprod{\mathbin{\square}} \newcommand\gbin[2]{\genfrac{[}{]}{0pt}{}{#1}{#2}} % % matrix theory % \newcommand\ip[2]{\langle#1,#2\rangle} \newcommand\one{{\bf1}} \DeclareMathOperator{\rk}{rk} \DeclareMathOperator{\tr}{tr} \DeclareMathOperator{\col}{col} \newcommand\mat[3]{\mathrm{Mat}_{#1\times #2}(#3)} \newcommand\sm[3]{\sum_{#1=#2}^{#3}} % % some group theory % \newcommand\aut[1]{{\rm Aut}(#1)} \newcommand\fx[1]{{\rm fix}(#1)}% ch2 \newcommand\grp[1]{\langle #1\rangle} \newcommand\nrml{\vartriangleleft} \newcommand\nrmleq{\trianglelefteq} \DeclareMathOperator{\Sym}{Sym} \newcommand\sym[1]{\Sym(#1)} \DeclareMathOperator{\Alt}{Alt} \newcommand\alt[1]{\Alt(#1)} \)

Section8.4Newton-Raphson

We can find a solution to our equation \(C(t) =\Phi(C(t))\) more efficiently by using Newton-Raphson. Note that \(\Phi\) is a power series (actually polynomial in \(u\)) and

\[\Phi(C_0+\de) \approx \Phi(C_0) +\Phi'(C_0)\de;\]
this works provided \(\de\) is divisible by a power of \(t\). So if \(C_0\) is an approximate solution to \(\Phi(C(t))=C(t)\), then our aim is to choose \(\de\) so that
\[C_0 + \de = \Phi(C_0) +\Phi'(C_0)\de,\]
which implies that
\[\de = \frac{\Phi(C_0)-C_0}{1-\Phi'(C_0)}.\]
Hence our proposed update formula is now
\[C_{n+1} = C_n + \frac{\Phi(C_n)-C_n}{1-\Phi'(C_n)}\]
Here
\[\Phi'(C_n(t)) = 2tC_n(t).\]

We can run a quick test. With

we find that the first 22 terms of nr(nr(nr(1+t))) are correct.

Your task is to write an efficient implementation of this method.