numbering a system of equations

Question

How can I add a number to the following system of equations so that the first equation take the number (1.a) and the second (1.b)?

\begin{equation}
\left\{
\begin{array}{l}
\begin{aligned}
x_k & = f_d(x_{k-1},u_{k-1},\theta) + q_{k-1}\\
y_k & = h(x_k,\theta,k) + r_k 
\end{aligned}
\end{array}
\right.
\label{eq:State}
\end{equation}

See the empheq package and combine that with the the subequations env from amsmath — daleif, Apr 25 '17 at 18:25
Related/duplicate: Equation numbering: how can I get (1.1), (2.1), (3.2) in the article class?; How to reference equations using letters and numbers — Werner, Apr 25 '17 at 18:26

score 4 · Answer 1 · answered Apr 25 '17 at 19:10

Use empheq to style your equation set, together with subequations to achieve your numbering objective:

\documentclass{article}

\usepackage{empheq,etoolbox}
% Update display of subequation numbering (Xy) > (X.y)
\patchcmd{\subequations}% <cmd>
  {\theparentequation\alph{equation}}% <search>
  {\theparentequation.\alph{equation}}% <replace>
  {}{}% <success><failure>

\begin{document}

\begin{subequations}
  \begin{empheq}[left=\empheqlbrace]{align}
    x_k &= f_d(x_{k-1},u_{k-1},\theta) + q_{k-1} \\
    y_k &= h(x_k,\theta,k) + r_k 
  \end{empheq}
\end{subequations}

\end{document}

The default numbering within subequations has the form (Xy). The etoolbox patch is applied in the preamble to change this to (X.y) for all subequations.

numbering a system of equations

1 Answers1