126

Here is my split equation:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{split}
a_{ijk} =& \frac {Pr(M_{I} =2  \&  M_J=1 \& M_K =1 | I=i , J=j , K=k)}{Pr (M_I =1 \& M_J =1 \& M_K=1 | I=i , J=j)} \\
            =& \frac {\mu_{ijk211}}{\mu_{ijk111}}\\
\end{split}
\end{equation}
\end{document}

I want to align this equation to the left. Is this possible in an equation environment?

1

7 Answers 7

120

I would not use the equation environment; rather, I would use flalign as such:
(notice the && at the end of each line)

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\noindent A \hfill Z
\begin{flalign}
a_{ijk} &= \frac {Pr(M_{I} =2  \&  M_J=1 \& M_K =1 | I=i , J=j , K=k)}{Pr (M_I =1 \& M_J =1 \& M_K=1 | I=i , J=j)}&&\\\nonumber
            &= \frac {\mu_{ijk211}}{\mu_{ijk111}}&&
\end{flalign}

\noindent A \hfill Z
\end{document}

Output

Another way to go is to set the fleqn option for the document class. However, this left-aligns all of your equations and hence should not be used when you want at least some equations to remain centered.

\documentclass[fleqn]{article}
\usepackage{amsmath}
\begin{document}
\noindent A \hfill Z
\begin{equation}
\begin{aligned}
a_{ijk} &= \frac {Pr(M_{I} =2  \&  M_J=1 \& M_K =1 | I=i , J=j , K=k)}{Pr (M_I =1 \& M_J =1 \& M_K=1 | I=i , J=j)}\\
            &= \frac {\mu_{ijk211}}{\mu_{ijk111}}\\
\end{aligned}
\end{equation}
\noindent A \hfill Z
\end{document}

For this output:

Output 2

As suggested by karlkoeller, if you want to get rid of the space between the left margin and the equation (to get a result similar to the first case), you should add \setlength{\mathindent}{0pt}. If you later want to indent it back to its default value, you can use the same command with a value of 15pt, which is the amount of pt a paragraph indent shifts its text to the right.

8
  • 16
    Or you could use the fleqn package option if you want all equations flush left. Eg: \usepackage[fleqn]{amsmath}.
    – Thruston
    Nov 18, 2013 at 17:40
  • @Thruston I was just editing my answer to add this possibility!
    – Ludovic C.
    Nov 18, 2013 at 17:40
  • 4
    This did not result in a left-align for me. And yes, I included \usepackage{amsmath}.
    – user124384
    Feb 7, 2018 at 17:06
  • 4
    If option 1 doesn't work for you, remember to add the && to the end of the line. That solved it for me. Aug 30, 2018 at 18:42
  • 2
    Reading @Armand Maree's comment is what finally clued me into the &&, after I spent 20 minutes searching online for why flalign was not working for me.
    – Joe
    Apr 12, 2020 at 15:26
78

Note: This doesn't answer the question exactly. But still try this solution first as it is probably the simplest.

Use align, and put & at the beginning of every line. Use \\ to separate multiple equations.

\begin{align*}
& a_{ijk} = 2 \\
&(because ||V_1-V_2|| = \max_{i \in [d]}|V^i_1 - V^i_2|)
\end{align*}

(This works if you want to left align a set of equations, but the whole equations could be at the center if your equations are short)

5
  • flalign is commonly used if you do not want to pass fleqn as a documentclass option. And the OP's aim was to have equations flush left.
    – TeXnician
    Nov 9, 2017 at 6:44
  • 4
    @TeXnician Fine. The reason why I added this answer is that this is the first answer googling "align equations left" gives. It doesn't answer OP exactly but still could be useful.
    – Binu Jasim
    Nov 9, 2017 at 6:52
  • @TeXnician I would not delete the answer, because it indeed be an answer. Nevertheless it is a very ugly hack, I would not recommend to use. I think in such cases voting should be preferred to tell the users which suggestion should be used and which not. Nov 9, 2017 at 8:44
  • 3
    Yeah, this helped me a lot
    – igorkf
    Feb 11, 2020 at 21:01
  • This helps a lot. You aren't able to \usepackage in MathJax but its really a struggle finding any information for workarounds for this kind of situation.
    – Uduru
    Jul 13, 2022 at 19:19
20

Put & at the beginning of the line for left alignment and \\ at the end of the line to break line. Enclose the equation between \begin(split) and \end(split)

\begin{equation}
\begin{split}
&T_{eff}=\sum_{i=1}^n f_i.t_i \\
&=h_1t_1+(1-h_1)h_2t_2+(1-h_1)(1-h_2)h_3t_3+...+ \\
&(1-h_1)(1-h_2)...(1-h_{n-1})h_nt_n
\end{split}
\end{equation}
1
  • 2
    What if my equation already involves the split environment? Apr 11, 2021 at 10:14
13

Alternatively, if one desires all equations in the document to be flushed left by default, one can also define in the preamble:

\usepackage[fleqn]{amsmath}

Then, proceed to use equation or align or similar environments.

0
7

Note flalign requires at least two groups of alignment, whence a supplementary ampersand. I wanted to point another possibility with the fleqn environment from nccmath (which loads amsmath). This environment can take an optional argument to set the distance from the left margin the equation(s) start (default is 0 pt). It works somewhat like the subequations environment in the sense that all (groups of) equations inside the environment will start at the left margin.

\documentclass{article}
\usepackage{amsmath, nccmath}
\usepackage{geometry}

\begin{document}

Some text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text.

\begin{fleqn}[\parindent]
\begin{equation}
\begin{split}
a_{ijk} =& \frac {Pr(M_{I} =2 \& M_J=1 \& M_K =1 | I=i , J=j , K=k)}{Pr (M_I =1 \& M_J =1 \& M_K=1 | I=i , J=j)} \\
            =& \frac {\mu_{ijk211}}{\mu_{ijk111}}\\
\end{split}
\end{equation}
\end{fleqn}

\begin{equation}
\begin{split}
a_{ijk} =& \frac {Pr(M_{I} =2 \& M_J=1 \& M_K =1 | I=i , J=j , K=k)}{Pr (M_I =1 \& M_J =1 \& M_K=1 | I=i , J=j)} \\
            =& \frac {\mu_{ijk211}}{\mu_{ijk111}}\\
\end{split}
\end{equation}
\end{document}

\end{document} 

enter image description here

2

multline* did the trick for me

\begin{multline*}
p(x) = 3x^6 + 14x^5y + 590x^4y^2 + 19x^3y^3\\ 
- 12x^2y^4 - 12xy^5 + 2y^6 - a^3b^3
\end{multline*}
0

It has been some time, but let me mention another way. You can use \hspace{10em} at the end of any line and within few try you can figure out what value (instead 10) works best.

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