7

Sought result except with numbering for the three different equations within the aligned subenvironment

I have tried all different sorts of solutions including align, aligned, cases and equation to have the result I get with this code except that I want numbering for the three lines in the aligned subenvironment. Do you have a solution or better way of representing this?

\begin{equation}
    \left\{
    \begin{aligned}
        \partial_t u(\vec{x},t) - \alpha \Delta u(\vec{x},t) &= f(\vec{x}), &&(\vec{x},t) \in \Omega \times J, \\
        %
        u(\vec{x},t) &= 0, &&(\vec{x},t) \in \partial \Omega \times J, \\
        %
        u(\vec{x},0) &=
        \begin{cases}
            \rho,   &\vec{x} \in T \\
            0,      &\vec{x} \in B \textbackslash T
        \end{cases}
        &&\vec{x} \in B
    \end{aligned}
    \right.
\end{equation}

2 Answers 2

7

With the use of the empheq package:

\documentclass{article}

\usepackage{empheq}
\begin{document}
    \begin{empheq}[left=\empheqlbrace]{align}
\partial_t u(\vec{x},t) - \alpha \Delta u(\vec{x},t)
    &= f(\vec{x}), &&(\vec{x},t) \in \Omega \times J, \\
%
u(\vec{x},t) &= 0, &&(\vec{x},t) \in \partial \Omega \times J, \\
%
u(\vec{x},0)
    & = \begin{cases}
    \rho,   &\vec{x} \in T \\
    0,      &\vec{x} \in B \setminus T
        \end{cases}
    &&\vec{x} \in B
    \end{empheq}
\end{document}

enter image description here

4
  • 1
    Don't use \textbackslash. Use \setminus instead.
    – Mico
    Dec 10, 2018 at 19:24
  • @Mico, ups, i didn't check used symbols :-(. corrected now. thank you very much!
    – Zarko
    Dec 10, 2018 at 19:46
  • @Mico, do you have an short explanation of why to use \setminus instead of \textbackslash? Dec 10, 2018 at 19:51
  • @RobinHellmers - \textbackslash is a text-mode command. In contrast, \setminus is a math-mode command. In your screenshot, note that the spacing around the backslash character is too tight, when compared to the screenshots posted by Zarko and myself.
    – Mico
    Dec 10, 2018 at 20:58
9

I don't think that much is gained by aligning the three equations on their respective = symbols. I'd left-align the expressions, using a numcases environment.

enter image description here

\documentclass{article}
\usepackage{newtxtext,newtxmath,mathrsfs} % optional
\usepackage{cases} % for 'numcases' env.
\begin{document}
\begin{numcases}{}
\partial_t u(\vec{x},t) - \alpha\Delta u(\vec{x},t) = f(\vec{x}), 
      &$(\vec{x},t)\in\Omega\times J$, \\
u(\vec{x},t) = 0, 
      &$(\vec{x},t)\in\partial\Omega\times J$, \\
u(\vec{x},0) =
          \left\{\begin{array}{@{}ll@{}}
          \rho,   &\vec{x} \in\mathscr{T} \\
          0,      &\vec{x} \in\mathscr{B}\setminus \mathscr{T}
          \end{array}\right.
      &$\vec{x} \in\mathscr{B}$
\end{numcases}
\end{document}

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