# How to include vertical dots between two equations?

How to include a vertical dots between two leftright arrows of equations, like in the picture below?

Here the code I used:

${\tilde{\pi}}_{x,t}-\theta_{x}\tilde{\pi}_{x,t-1}=\frac{(1-\zeta_x \beta)(1 \zeta_x)}{\zeta_x (\widetilde{rmc}_{x,t}+\tilde{v}_{x,t})+\beta(E_t\tilde{\pi}_{x,t+1}-\theta_{x}\tilde{\pi}_{x,t})$

\Leftrightarrow

\Leftrightarrow

${\tilde{\pi}}_{x,t}=\frac{\theta_{x}}{1+\beta \theta_{x}}\tilde{\pi}_{x,t-1}+\frac{\beta}{1+\beta \theta_{x}}E_{t}\tilde{\pi}_{x,t+1}+\frac{(1-\zeta_x \beta)(1-\zeta_x)}{\zeta_x(1+\beta \theta_{x})}(\widetilde{rmc}_{x,t}-\widetilde{P}^{X*}_t-\tilde{rs_t}+\tilde{v}_{x,t})$


and my output:

You can use the align environment (from amsmath) and the \vdotswithin command from the mathtools package:

\documentclass{article}
\usepackage{mathtools}

\begin{document}

\begin{align*}
{\tilde{\pi}}_{x,t} & - \theta_{x}\tilde{\pi}_{x,t-1} =
\frac{(1-\zeta_x \beta)(1 \zeta_x)}{\zeta_x} (\widetilde{rmc}_{x,t}+\tilde{v}_{x,t})+\beta(E_t\tilde{\pi}_{x,t+1}-\theta_{x}\tilde{\pi}_{x,t})\\
& \Leftrightarrow\\
& \vdotswithin{\Leftrightarrow}\\
& \Leftrightarrow\\
{\tilde{\pi}}_{x,t} & =\frac{\theta_{x}}{1+\beta \theta_{x}}
\tilde{\pi}_{x,t-1} +
\frac{\beta}{1+\beta \theta_{x}} E_{t} \tilde{\pi}_{x,t+1} +
\frac{(1-\zeta_x \beta)(1-\zeta_x)}{\zeta_x(1+\beta \theta_{x})}(\widetilde{rmc}_{x,t}-\widetilde{P}^{X*}_t-\tilde{rs_t}+\tilde{v}_{x,t})
\end{align*}

\end{document}


The output will look like this:

Another way of structuring the calculation using gather and aligned from the amsmath package.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{gather*}
{\tilde{\pi}}_{x,t}-\theta_{x}\tilde{\pi}_{x,t-1}
=\frac{(1-\zeta_x \beta)(1 \zeta_x)}{\zeta_x} (\widetilde{rmc}_{x,t}+\tilde{v}_{x,t})
+\beta(E_t\tilde{\pi}_{x,t+1}-\theta_{x}\tilde{\pi}_{x,t})\\
\Leftrightarrow\\
\vdots\\
\Leftrightarrow\\
\begin{aligned}
{\tilde{\pi}}_{x,t}={}
&\frac{\theta_{x}}{1+\beta \theta_{x}}\tilde{\pi}_{x,t-1}
+\frac{\beta}{1+\beta \theta_{x}}E_{t}\tilde{\pi}_{x,t+1}\\
&+\frac{(1-\zeta_x \beta)(1-\zeta_x)}{\zeta_x(1+\beta \theta_{x})}
(\widetilde{rmc}_{x,t}-\widetilde{P}^{X*}_t-\tilde{rs_t}+\tilde{v}_{x,t})
\end{aligned}
\end{gather*}
\end{document}