How can I align this equation in the center?

Question

disclaimer: I'm very new with LaTeX.

I have an equation and by default it is align to right right side (not sure why, I thought the left is usually the default). I want it aligned on the left or center.

My code is:

\begin{equation}
\begin{split}
Gest = \\69.73 s^{11} + 2.546e04 s^{10} + 4.948e06 s^9 + 6.943e08 s^8 + 7.08e10 s^7 + 4.952e12 s^6 + 2.304e14 s^5 \\+ 7.106e15 s^4 + 1.455e17 s^3 + 1.89e18 s^2 + 1.259e19 s + 3.154e19 \\-----------------------------------\\ 0.01592 s^{15} + 5.822 s^{14} + 1372 s^{13} + 2.441e05 s^{12} + 3.255e07 s^{11} + 3.408e09 s^{10}\\ + 2.819e11 s^9 + 1.744e13 s^8 + 7.626e14 s^7 + 2.296e16 s^6 + 4.712e17 s^5 + 6.318e18 s^4 \\+ 4.729e19 s^3 + 1.696e20 s^2 + 2.305e20 s + 8.076e19
    \label{}
\end{split}
\end{equation}

I already tried:

• \begin{flushleft}...\end{flushleft} (does not work)
• \begin{align*}...\end{align*} (returns error)

but no success. Could not find anything else. Any advice?

Answer 1

A possible solution, but I think it would be better to give a name to numerator and denominator and the writing the fraction with those symbols.

\documentclass[a4paper]{article}
\usepackage{geometry}
\usepackage{amsmath}
\usepackage{siunitx}

\begin{document}

\begin{equation}
\mathit{Gest} =
\frac{
  \begin{aligned}
  &
  \num{69.73} s^{11} + \num{2.546e04} s^{10} + \num{4.948e06} s^9 + \num{6.943e08} s^8 \\
  &+
  \num{7.08e10} s^7 + \num{4.952e12} s^6 + \num{2.304e14} s^5 + \num{7.106e15} s^4 \\
  &+
  \num{1.455e17} s^3 + \num{1.89e18} s^2 + \num{1.259e19} s + \num{3.154e19}
  \end{aligned}
}{
  \begin{aligned}
  &
  \num{0.01592} s^{15} + \num{5.822} s^{14} + \num{1372} s^{13} + \num{2.441e05} s^{12} \\
  &+
  \num{3.255e07} s^{11} + \num{3.408e09} s^{10} + \num{2.819e11} s^9 + \num{1.744e13} s^8 \\
  &+
  \num{7.626e14} s^7 + \num{2.296e16} s^6 + \num{4.712e17} s^5 + \num{6.318e18} s^4 \\
  &+
  \num{4.729e19} s^3 + \num{1.696e20} s^2 + \num{2.305e20} s + \num{8.076e19}
  \end{aligned}
}
\end{equation}

\end{document}

\documentclass[a4paper]{article}
\usepackage{geometry}
\usepackage{amsmath}
\usepackage{siunitx}

\begin{document}

\begin{equation}
\begin{gathered}
\mathit{Gest} = \frac{A}{B} \\
\begin{aligned}
A &=
  \begin{aligned}[t]
  &
  \num{69.73} s^{11} + \num{2.546e04} s^{10} + \num{4.948e06} s^9 + \num{6.943e08} s^8 \\
  &+
  \num{7.08e10} s^7 + \num{4.952e12} s^6 + \num{2.304e14} s^5 + \num{7.106e15} s^4 \\
  &+
  \num{1.455e17} s^3 + \num{1.89e18} s^2 + \num{1.259e19} s + \num{3.154e19}
  \end{aligned}
\\
B &=
  \begin{aligned}[t]
  &
  \num{0.01592} s^{15} + \num{5.822} s^{14} + \num{1372} s^{13} + \num{2.441e05} s^{12} \\
  &+
  \num{3.255e07} s^{11} + \num{3.408e09} s^{10} + \num{2.819e11} s^9 + \num{1.744e13} s^8 \\
  &+
  \num{7.626e14} s^7 + \num{2.296e16} s^6 + \num{4.712e17} s^5 + \num{6.318e18} s^4 \\
  &+
  \num{4.729e19} s^3 + \num{1.696e20} s^2 + \num{2.305e20} s + \num{8.076e19}
  \end{aligned}
\end{aligned}
\end{gathered}
\end{equation}

\end{document}

Answer 2

(edited to reflect the OP's comment that "the dash lines where to make it look like an fraction")

The following solution uses a \frac directive, with \parboxes in the numerator and denominator; that way, LaTeX is free to find suitable line breaks on its own.

\documentclass{article}
\usepackage{amsmath}
\newcommand\mybox[1]{\parbox{0.75\textwidth}{\centering $#1$}}
\begin{document}
\begin{equation} \label{}
Gest = \frac{\mybox{69.73 s^{11} + 2.546e04 s^{10} + 4.948e06 s^9 + 
6.943e08 s^8 + 7.08e10 s^7 + 4.952e12 s^6 + 2.304e14 s^5 +
7.106e15 s^4 + 1.455e17 s^3 + 1.89e18 s^2 + 1.259e19 s +
3.154e19}}{\mybox{0.01592 s^{15} + 5.822 s^{14} + 1372 s^{13} + 
2.441e05 s^{12} + 3.255e07 s^{11} + 3.408e09 s^{10} + 
2.819e11 s^9 + 1.744e13 s^8 + 7.626e14 s^7 + 2.296e16 s^6 +
4.712e17 s^5 + 6.318e18 s^4 + 4.729e19 s^3 + 1.696e20 s^2 +
2.305e20 s + 8.076e19}}
\end{equation}
\end{document}

---

Addendum: All those 2.546e04-like terms are not visually satisfying. I suggest you also load the siunitx package and encase the numbers in \num{...} wrappers. (Aside: the \mathstrut directives are there to generate more visual separation around the fraction line.)

\documentclass{article}
\usepackage{amsmath,siunitx}
\sisetup{exponent-product={{}\cdot{}},tight-spacing}

\newcommand\mybox[1]{\parbox{0.79\textwidth}{\centering $#1$}}
\begin{document}
\begin{equation} \label{}
Gest = \frac{\mybox{69.73 s^{11} + \num{2.546e04} s^{10} + \num{4.948e06} s^9 + \num{6.943e08} s^8 + \num{7.08e10} s^7 + \num{4.952e12} s^6 + \num{2.304e14} s^5 + \num{7.106e15} s^4 + \num{1.455e17} s^3 + \num{1.89e18} s^2 + \num{1.259e19} s + \num{3.154e19}_{\mathstrut}}}{%
\mybox{0.01592 s^{15} + 5.822 s^{14^{\mathstrut}} + 1372 s^{13} + \num{2.441e05} s^{12} + \num{3.255e07} s^{11} + \num{3.408e09} s^{10} + \num{2.819e11} s^9 + \num{1.744e13} s^8 + \num{7.626e14} s^7 + \num{2.296e16} s^6 + \num{4.712e17} s^5 + \num{6.318e18} s^4 + \num{4.729e19} s^3 + \num{1.696e20} s^2 + \num{2.305e20} s + \num{8.076e19}}}
\end{equation}
\end{document}

Answer 3

You need to use the alignment character & to specify where it should be aligned. I also included the space \quad to align after the =.

\documentclass{article}
\usepackage{lipsum}
\usepackage{amsmath}
\begin{document}
\begin{equation}
  \begin{split}
    G_{\text{est}} &= 69.73 s^{11} + 2.546e04 s^{10} + 4.948e06 s^9 + 6.943e08 s^8 + 7.08e10 s^7 + 4.952e12 s^6 + 2.304e14 s^5 \\
    &\quad + 7.106e15 s^4 + 1.455e17 s^3 + 1.89e18 s^2 + 1.259e19 s + 3.154e19 \\
    &\quad -----------------------------------\\ 
    &\quad +0.01592 s^{15} + 5.822 s^{14} + 1372 s^{13} + 2.441e05 s^{12} + 3.255e07 s^{11} + 3.408e09 s^{10}\\ 
    &\quad + 2.819e11 s^9 + 1.744e13 s^8 + 7.626e14 s^7 + 2.296e16 s^6 + 4.712e17 s^5 + 6.318e18 s^4 \\
    &\quad + 4.729e19 s^3 + 1.696e20 s^2 + 2.305e20 s + 8.076e19
    \label{eq:longeq}
  \end{split}
\end{equation}
\end{document}

Still, the lines are too long, at least with the default text width settings. Also, to get the numbering on the last row I would prefer align. (Since I did not understand the dashed line I removed it.)

\begin{align}
  G_{\text{est}} &= 69.73 s^{11} + 2.546e04 s^{10} + 4.948e06 s^9 + 6.943e08 s^8 + 7.08e10 s^7 \nonumber\\
  &\quad + 4.952e12 s^6 + 2.304e14 s^5 + 7.106e15 s^4 + 1.455e17 s^3 + 1.89e18 s^2 \nonumber\\
  &\quad + 1.259e19 s + 3.154e19 + 0.01592 s^{15} + 5.822 s^{14} + 1372 s^{13} \nonumber\\
  &\quad + 2.441e05 s^{12} + 3.255e07 s^{11} + 3.408e09 s^{10} + 2.819e11 s^9 + 1.744e13 s^8 \nonumber\\
  &\quad + 7.626e14 s^7 + 2.296e16 s^6 + 4.712e17 s^5 + 6.318e18 s^4 + 4.729e19 s^3 \nonumber\\
  &\quad + 1.696e20 s^2 + 2.305e20 s + 8.076e19
  \label{eq:longeq}
\end{align}

EDIT

With the dashed line denoting a fraction I would do something like this.

\begin{equation}
  \label{eq:1}
  G_{\text{est}}=\frac{G_1}{G_2}
\end{equation}
where 
\begin{align}
  G_1 &= 69.73 s^{11} + 2.546e04 s^{10} + 4.948e06 s^9 + 6.943e08 s^8 + 7.08e10 s^7 \nonumber\\
  &\quad + 4.952e12 s^6 + 2.304e14 s^5 + 7.106e15 s^4 + 1.455e17 s^3 + 1.89e18 s^2 \nonumber\\
  &\quad + 1.259e19 s + 3.154e19 \\
  G_2 &= 0.01592 s^{15} + 5.822 s^{14} + 1372 s^{13} + 2.441e05 s^{12} + 3.255e07 s^{11} \nonumber\\
  &\quad + 3.408e09 s^{10} + 2.819e11 s^9 + 1.744e13 s^8 + 7.626e14 s^7 \nonumber\\
  &\quad + 2.296e16 s^6 + 4.712e17 s^5 + 6.318e18 s^4 + 4.729e19 s^3 \nonumber\\
  &\quad + 1.696e20 s^2 + 2.305e20 s + 8.076e19
\end{align}