# Split moves my equations to the left. Why?

Why does split move my equation to the left in the following code?

\begin{equation*}
\begin{split}
\|V(\varphi)(t)-V(\psi)(t)\|
& =  \Big\|\int_{t_0}^t  [f(s,\varphi(s))-f(s,\psi(s))]ds \Big\| \leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} \|f(s,\varphi(s))-f(s,\psi(s))\|ds
\\  \leq
\int_{\min\{t_0,t\}}^{\max\{t_0,t\}} L \|\varphi(s)-\psi(s)\|ds
& =  L \int_{\max\{t_0,t\}}^{\max\{t_0,t\}} \|\varphi(s)-\psi(s)\|e^{-R(s-t_0)}e^{R(s-t_0)}ds \leq \\ \leq L\|\varphi-\psi\|_B \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} e^{R(s-t_0)}ds & a
\end{split}
\end{equation*}


Ideally, I would like all lines to begin at the same point, but currently I get the following output:

• you are aligning on = the part before the alignment aligns to the right, the part after the alignment aligns to the left. so you get the layout you show, it isn't clear what layout you want instead, perhaps alignedat with alignment points on every \leq and every = ? Commented Apr 3, 2018 at 14:35
• GuM's answer is the right one, as it also fixes the small mistakes you have in your code. The normal practice is to not repeat the relation symbol at the end of a line. I see no reason for having three parts in the first line, symmetry wants just one piece per line (and just two in the first one). Commented Apr 3, 2018 at 15:47

Split is used to split the equation in two parts and align them to &.

New line is the \\ and at every line you have a part left of the & and one right of it

So your code could be like this (added some & and \\ in appropriate places):

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}
\begin{document}
$\begin{split} \|V(\varphi)(t)-V(\psi)(t)\| & = \Big\|\int_{t_0}^t [f(s,\varphi(s))-f(s,\psi(s))]ds \Big\| \leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} \|f(s,\varphi(s))-f(s,\psi(s))\|ds \leq \\ &\leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} L \|\varphi(s)-\psi(s)\|ds =\\ & = L \int_{\max\{t_0,t\}}^{\max\{t_0,t\}} \|\varphi(s)-\psi(s)\|e^{-R(s-t_0)}e^{R(s-t_0)}ds \leq \\ &\leq L\|\varphi-\psi\|_B \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} e^{R(s-t_0)}ds {\color{red} a} \end{split}$
\end{document}


Output:

PS: The red \alpha is something I didn't knew what to do (thus red)

Also didn't used your equation*

I think that what you really mean is this:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly
% declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}

\begin{document}

\begin{equation*}
\begin{split}
\lVert V(\varphi)(t)-V(\psi)(t)\rVert
&=  \Bigl\|\int_{t_0}^t  [f(s,\varphi(s))-f(s,\psi(s))] \,ds \Bigr\| \\
&\leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} \lVert f(s,\varphi(s))-f(s,\psi(s))\rVert \,ds \\
&\leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} L \lVert\varphi(s)-\psi(s)\rVert \,ds \\
&=  L \int_{\max\{t_0,t\}}^{\max\{t_0,t\}} \lVert\varphi(s)-\psi(s)\rVert e^{-R(s-t_0)}e^{R(s-t_0)} \,ds \\
&\leq L\lVert\varphi-\psi\rVert_B \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} e^{R(s-t_0)}\,ds
\end{split}
\end{equation*}

\end{document}


Note that I took the liberty of replacing \Big\| ... \Big\| with \Bigl\| ... \Bigr\|, to replace other instances of \| with \lVert and \rVert as appropriate, and to add a thin space before ds. I haven’t checked for other possible istances of poor LaTeX coding. :-)

A variant, with an aligned environment nested in an align*. In addition, I simplified the typing of the norms with the \DeclarePairedDelimiter from mathtools:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[showframe]{geometry}
\usepackage{amssymb, mathtools}
\DeclarePairedDelimiter\norm\lVert\rVert

\begin{document}

\begin{align*}
\norm[\big]{V(\varphi)(t)-V(\psi)(t)}
= \norm[\Big]{\int_{t_0}^t \bigl[f(s,\varphi(s))-f(s,\psi(s))\bigr]ds }\leq \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} \norm[\big]{f(s,\varphi(s))-f(s,\psi(s))}\,ds\\
\mathllap{\begin{aligned}& \leq
\int_{\min\{t_0,t\}}^{\max\{t_0,t\}} L {\norm[\big]{\varphi(s)-\psi(s)}}\,ds%[\big]
= L \int_{\max\{t_0,t\}}^{\max\{t_0,t\}}{ \norm[\big]{\varphi(s)-\psi(s)}}e^{-R(s-t_0)}e^{R(s-t_0)}\,ds
\\
& \leq L{\norm{\varphi-\psi}_B} \int_{\min\{t_0,t\}}^{\max\{t_0,t\}} e^{R(s-t_0)}\,ds
\end{aligned}}
\end{align*}

\end{document}