diff --git a/Manuscript/EPAWTFT.tex b/Manuscript/EPAWTFT.tex index e75d624..bbccec3 100644 --- a/Manuscript/EPAWTFT.tex +++ b/Manuscript/EPAWTFT.tex @@ -1250,7 +1250,33 @@ More specifically, a $[d_A/d_B]$ Pad\'e approximant is defined as (with $b_0 = 1$), where the coefficients of the polynomials $A(\lambda)$ and $B(\lambda)$ are determined by collecting terms according to power of $\lambda$. Pad\'e approximants are extremely useful in many areas of physics and chemistry \cite{Loos_2013,Pavlyukh_2017,Tarantino_2019,Gluzman_2020} as they can model poles, which appears at the roots of the polynomial $B(\lambda)$. However, they are unable to model functions with square-root branch points, which are ubiquitous in the singularity structure of a typical perturbative treatment. -Figure \ref{fig:PadeRMP} illustrates the improvement brought by diagonal (\ie, $d_A = d_B$) Pad\'e approximants as compared to the usual Taylor expansion in the case of the RMP series of the Hubbard dimer for $U/t = 4.5$. +Figure \ref{fig:PadeRMP} illustrates the improvement brought by diagonal (\ie, $d_A = d_B$) Pad\'e approximants as compared to the usual Taylor expansion in cases where the RMP series of the Hubbard dimer converges ($U/t = 3.5$) and diverges ($U/t = 4.5$). + +\begin{table} + \caption{RMP ground-state energy estimate at $\lambda = 1$ provided by various Taylor expansions and Pad\'e approximants at $U/t = 3.5$ and $4.5$. + We also report the estimate of the radius of convergence $r_c$ provided by the diagonal Pad\'e approximants. + \label{tab:PadeRMP}} + \begin{ruledtabular} + \begin{tabular}{lccccc} + & & \mc{2}{c}{$r_c$} & \mc{2}{c}{$E_{-}(\lambda = 1)$} \\ + \cline{3-4} \cline{5-6} + Method & degree & $U/t = 3.5$ & $U/t = 4.5$ & $U/t = 3.5$ & $U/t = 4.5$ \\ + \hline + Taylor & 2 & & & $-1.01563$ & $-1.01563$ \\ + & 3 & & & $-1.01563$ & $-1.01563$ \\ + & 4 & & & $-0.86908$ & $-0.61517$ \\ + & 5 & & & $-0.86908$ & $-0.61517$ \\ + & 6 & & & $-0.92518$ & $-0.86858$ \\ + Pad\'e & [1/1] & $2.29$ & $1.78$ & $-1.61111$ & $-2.64286$ \\ + & [2/2] & $2.29$ & $1.78$ & $-0.82124$ & $-0.48446$ \\ + & [3/3] & $1.73$ & $1.34$ & $-0.91995$ & $-0.81929$ \\ + & [4/4] & $1.47$ & $1.14$ & $-0.90579$ & $-0.74866$ \\ + & [5/5] & $1.35$ & $1.05$ & $-0.90778$ & $-0.76277$ \\ + \hline + Exact & & $1.14$ & $0.89$ & $-0.90754$ & $-0.76040$ \\ + \end{tabular} + \end{ruledtabular} +\end{table} %%%%%%%%%%%%%%%%% \begin{figure*} @@ -1306,23 +1332,24 @@ However, by ramping up high enough the degree of the polynomials, one is able to %%%%%%%%%%%%%%%%% \begin{table} - \caption{Radius of convergence $r_c$ for various resummation techniques at $U/t = 3$ and $7$. - The truncation degree of the Taylor expansion $n$ of $E(\lambda)$ and the number of branch points $n_\text{bp} = \max(2d_p,d_q+d_r)$ generated by the quadratic approximant are also reported. + \caption{Estimate of the radius of convergence $r_c$ of the UMP energy function provided by various resummation techniques at $U/t = 3$ and $7$. + The truncation degree of the Taylor expansion $n$ of $E(\lambda)$ and the number of branch points $n_\text{bp} = \max(2d_p,d_q+d_r)$ generated by the quadratic approximants are also reported. \label{tab:QuadUMP}} \begin{ruledtabular} - \begin{tabular}{llcccc} - & & & & \mc{2}{c}{$r_c$} \\ - \cline{5-6} - \mc{2}{c}{Method} & $n$ & $n_\text{bp}$ & $U/t = 3$ & $U/t = 7$ \\ + \begin{tabular}{lccccccc} + & & & & \mc{2}{c}{$r_c$} & \mc{2}{c}{$E_{-}(\lambda)$} \\ + \cline{5-6}\cline{7-8} + \mc{2}{c}{Method} & $n$ & $n_\text{bp}$ & $U/t = 3$ & $U/t = 7$ & $U/t = 3$ & $U/t = 7$ \\ \hline - Pad\'e & [2/2] & 4 & & 0.97448 & 1.00030 \\ - & [3/3] & 6 & & 1.14138 & 1.00448 \\ - Quadratic & [2/1,2] & 6 & 4 & 1.08640 & 1.00310 \\ - & [2/2,2] & 7 & 4 & 1.08193 & 1.00310 \\ - & [3/2,2] & 8 & 6 & 1.08247 & 1.00106 \\ - & [3/2,3] & 9 & 6 & 1.07069 & 1.00239 \\ - & [3/3,3] & 10 & 6 & 1.07064 & 1.00239 \\ - Exact & & & & 1.06917 & 1.00239\\ + Pad\'e & [2/2] & 4 & & 0.974 & 1.000 \\ + & [3/3] & 6 & & 1.141 & 1.004 \\ + & [4/4] & 8 & & 1.068 & 1.003 \\ + Quadratic & [2/1,2] & 6 & 4 & 1.086 & 1.003 \\ + & [2/2,2] & 7 & 4 & 1.082 & 1.003 \\ + & [3/2,2] & 8 & 6 & 1.082 & 1.001 \\ + & [3/2,3] & 9 & 6 & 1.071 & 1.002 \\ + & [3/3,3] & 10 & 6 & 1.071 & 1.002 \\ + Exact & & & & 1.069 & 1.002 \\ \end{tabular} \end{ruledtabular} \end{table} diff --git a/Manuscript/PadeRMP35.pdf b/Manuscript/PadeRMP35.pdf index 3be5d09..fb239b1 100644 Binary files a/Manuscript/PadeRMP35.pdf and b/Manuscript/PadeRMP35.pdf differ diff --git a/Manuscript/PadeRMP45.pdf b/Manuscript/PadeRMP45.pdf index 059a0b4..6dca710 100644 Binary files a/Manuscript/PadeRMP45.pdf and b/Manuscript/PadeRMP45.pdf differ