alignhorizontal alignmentmath-mode
I have a list of boundary conditions which I would like to display using aligned environment. Here is the code so far:
\begin{equation}
\left.\begin{aligned}
x&=y &\text{in...},\\\
x'&=y' &\text{in...}, \\\
x''&=y''&\text{in...}, \\\
x'''&=y'''&\text{in....}\\\
\end{aligned}\right\}
\end{equation}
I want the equations on the LHS to be aligned at the = sign, but I also want the start of each condition (in...) to be aligned at in. Does anyone know how I can do this?
I would't use center alignment for the three equations: either you align them at the equals sign or left align them because of the side conditions. I wouldn't put the conditions too far from the equations, either: the conditions are part of the equations, after all. A \quad or \qquad seems sufficient.
\documentclass{article}
\usepackage{amsmath}
\numberwithin{equation}{section}
\begin{document}
\section{Outflow}
For the outflow boundary condition, the pressure is specified as a Dirichlet boundary
condition, assigned with free-stream pressure and the density $\rho$ and the velocity
$\vec{u}$ are specified as a Neumann boundary condition,
\begin{alignat}{2}
&p = p_\infty\qquad && \text{on $\Gamma_{\mathrm{out}}$} \\
&\frac{\partial\rho}{\partial\hat{n}} = 0 && \text{on $\Gamma_{\mathrm{out}}$} \\
&\frac{\partial \vec{u}}{\partial \hat{n}} = 0 && \text{on $\Gamma_{\mathrm{out}}$}
\end{alignat}
\end{document}
If you want alignment on the equals signs, just change the position of the first &:
\documentclass{article}
\usepackage{amsmath}
\numberwithin{equation}{section}
\begin{document}
\section{Outflow}
For the outflow boundary condition, the pressure is specified as a Dirichlet boundary
condition, assigned with free-stream pressure and the density $\rho$ and the velocity
$\vec{u}$ are specified as a Neumann boundary condition,
\begin{alignat}{2}
p &= p_\infty\qquad && \text{on $\Gamma_{\mathrm{out}}$} \\
\frac{\partial\rho}{\partial\hat{n}} &= 0 && \text{on $\Gamma_{\mathrm{out}}$} \\
\frac{\partial \vec{u}}{\partial \hat{n}} &= 0 && \text{on $\Gamma_{\mathrm{out}}$}
\end{alignat}
\end{document}
My personal preference goes to the first solution.
If you measure the left part in the last line and right part in the first line, you find that their sum exceeds the line width.
The align environment will never make two columns overlap. You might exploit the particular case, where the longer text will fit in the first line even if a small overlap with the final line appears.
Not a general method, I'm afraid: each elephant needs its particular method to be stuffed in a suitcase.
I tried with \hspace{-2em} without success. With \hspace{-2.5em} the amount of overlap is smaller.
\documentclass[12pt, letterpaper]{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
&f'(0)=\lim_{x\to 0} \frac{f(x)-f(0)}{x-0}
&\text{\hspace{-3em}limit definition of derivative}\\
&=\lim_{x\to 0} \frac{x^2 \sin\left(\frac{1}{x}\right)}{x}
=\lim_{x\to 0} x\sin\left(\frac{1}{x}\right)
&\text{simplifying the limit}\\
&0\leq\left| \sin \left(\frac{1}{x}\right) \right| \leq 1 \implies
0\leq \left|x \sin \left(\frac{1}{x}\right)\right|\leq \lvert x\rvert
&\text{bound for sine}
\end{align}
\end{document}
Avoid \left and \right unless necessary (and consider that they essentially only work well with fractions or arrays).
Also \limits is to be very rarely used when doing inline math and does nothing when in display math.
Best Answer
You need an additional
&to switch the alignment: