Left align equation in equation enviroment

Question

I would like to left align a set of equation like this:

\begin{equation}
C_{DLP}=C_{Pre-processing}+C_{Production}+C_{Material}+C_{Post-processing}+C_{Overhead} \end{equation}
$Where$
\begin{equation}
C_{Pre-processing}= C_O \times T_{SW}
\end{equation}

\begin{equation}
C_{Production}= C_M \times T_{B}
\end{equation}

\begin{equation}
C_{Material}= C_{M_kg} \times V
\end{equation}

\begin{equation}
C_{Post-processing}= C_O \times T_{Post-processing}
\end{equation}

\begin{equation}
C_{Overhead}= C_{El} + C_{Sr} + C_{Me}
\end{equation}

How can I do it?

Answer 1

If you do not left align the rest of your document's equations, I would not start this just for this case. I would recommend to use align as shown many times on this site.

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{align}
\begin{split}
C_{\text{DLP}}&=C_{\text{Pre-processing}} + C_{\text{Production}} \\ 
&\quad+ C_{\text{Material}} + C_{\text{Post-processing}}+C_{\text{Overhead}}
\end{split}
\shortintertext{Where}
C_{\text{Pre-processing}} &= C_O \times T_{SW}\\
C_{\text{Production}} &= C_M \times T_{B}\\
C_{\text{Material}}&= C_{M_kg} \times V\\
C_{\text{Post-processing}}&= C_O \times T_{\text{Post-processing}}\\
C_{\text{Overhead}}&= C_{El} + C_{Sr} + C_{Me}
\end{align}
\end{document}

Answer 2

To left-align all equations, use the fleqn option of amsmath. If you want only a group of equations to be left-aligned, you can use the fleqn environment of nccmath, which works like the subequations environment. It accepts an optional argument to specify the left margin of the environment. I took the liberty to set most indices in text mode, as semantically they're texts:

\documentclass{article}
\usepackage{mathtools, nccmath}
\usepackage[showframe]{geometry}%

\begin{document}

\begin{fleqn}[\parindent]
\begin{subequations}
  \begin{align}
      & C_{DLP}=C_\mathrm{Pre-processing}+C_\mathrm{Production}+C_\mathrm{Material}+C_\text{Post-processing}+C_\mathrm{Overhead} \\ \shortintertext{Where}
      & C_\mathrm{Pre-processing}= C_O × T_{SW} \\
      & C_\mathrm{Production}= C_M × T_{B} \\\
      & C_\mathrm{Material}= C_\mathrm{M_{kg}} × V
  \end{align}
\end{subequations}
\end{fleqn}
\vspace{4ex}
\begin{gather}
  C_\mathrm{Post-processing}= C_O × T_\text{Post-processing}\\
  C_\mathrm{Overhead}= C_\mathrm{El} + C_\mathrm{Sr} + C_\mathrm{Me}
\end{gather}

\end{document}