Sstrhsrtj

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?

I would not use the equation environment; rather, I would use flalign as such:

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}

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:

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.

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)

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}

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*}

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}