Centering Aligned Equations

Question

I have equations that are aligned by their equals signs. I want to center the aligned equals symbols on the page. Any ideas? I'm all out of them.

EDIT: There was a typo in the second equation. I forgot the & to the left of =. What I'm looking for is to center the aligned = on the page so that all of the aligned = run down the middle of the page.

\begin{align*}
0.01&=1-P(Z_i<c_1)\\
P(Z_i<c_1)&=0.99
\end{align*}

Answer 1

Hm, quite unusual demand. Your wish require manual tweaking of equation positioning, for example with use of the \phantom macro:

\documentclass[a4paper,12pt]{article}
%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{amsmath}

\begin{document}
\begin{align*}
                    0.01    & = 1 - P(Z_i<c_1)\\
\hphantom{1 - P}(Z_i<c_1)   & = 0.99
\end{align*}
\begin{align}
                    0.01    & = 1 - P(Z_i<c_1)\\
\hphantom{1 - P}(Z_i<c_1)   & = 0.99
\end{align}
\end{document}

(red lines shows text borders)

or use the following unusual construction of nonnumbered equation system writen in tabularx table:

\documentclass[a4paper,12pt]{article}
%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{amsmath}
\usepackage{tabularx}
\newcolumntype{L}{>{\raggedright\arraybackslash$}X<{$}}
\newcolumntype{R}{>{\raggedleft\arraybackslash$} X<{$}}

\begin{document}
\[\setlength\tabcolsep{2pt}
\begin{tabularx}{\linewidth}{R >{$}c<{$} L}
    0.01    & = & 1 - P(Z_i<c_1)  \\
(Z_i<c_1)   & = & 0.99
\end{tabularx}
\]
\end{document}

Answer 2

I have put only another &. Like this?

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}


\begin{document}
\begin{align*}
0.01&=1-P(Z_i<c_1)\\
P(Z_i<c_1)&=0.99
\end{align*}
\end{document}

Answer 3

You can use \mathllap and \mathrlap, and combine them to a macro that truly centers the = sign.

\documentclass{article}
\usepackage{mathtools}
\newcommand{\dclap}[2]{\mathllap{#1}&=\mathrlap{#2}}
\begin{document}
\begin{align*}
\dclap{0.01}{1-P(Z_i<c_1)}\\
\dclap{P(Z_i<c_1)}{0.99}\\
\dclap{\text{something really wide}}{\pi}
\end{align*}
\end{document}