Hcfyk

I want to break this equation in multi-line but unable to get it!

documentclass{article}

usepackage{amsmath}

DeclareMathOperator{E}{E}

begin{document}

begin{multline*}

P_t=

frac{1}{2}Bigl(m_t+v_t-u_t

+(frac{1-zeta }{2})(frac{E_{t-1}m_t+frac{1-zeta }{2zeta }E_{t- 

2}m_t+frac{zeta (1-zeta )}{2(1+zeta )}E_{t-2}P_{t-1}+frac{zeta } 

{2}P_{t-1}+frac{zeta }{1+zeta }P_{t-2}}{(1+zeta )}))bigr\

+frac{(1-zeta )}{4}Bigl(frac{E_{t-2}m_t+(frac{zeta }{2})(E_{t-2}P_{t- 

1}+P_{t-2})}{(1+zeta )})Bigr) \

+frac{zeta }{4}(Bigl((P_{t-1}+P_{t-2})Bigr)

end{multline*}

end{document}

It's getting out of the mage, so I tired to break it but still it's not showing the correct showing. Can anyone help to identify the problem in coding? How to use breqn?

You overuse parentheses. If I've well understood your formula, here is a layout which fits on two lines, with the geometry package, to have more decent margins. Also, I prefer to use the medium-size fractions from nccmath for fractionary coefficients:

documentclass{article}

usepackage[showframe]{geometry}

usepackage{amsmath, nccmath}

DeclareMathOperator{E}{E}



begin{document}

vspace*{2ex}

begin{multline*}

P_t=

mfrac{1}{2}biggl(m_t+v_t-u_t

+frac{1-zeta }{2},frac{E_{t-1}m_t+frac{1-zeta }{2zeta }E_{t-2}m_t+frac{zeta (1-zeta )}{2(1+zeta )}E_{t-2}P_{t-1}+frac{zeta }{2}P_{t-1} +frac{zeta }{1+zeta }P_{t-2}}{1+zeta}biggr) \

+frac{1-zeta }{4},frac{E_{t-2}m_t+frac{zeta }{2}(E_{t-2}P_{t-1}+P_{t-2})}{1+zeta} +frac{zeta }{4}(P_{t-1}+P_{t-2})

end{multline*}



end{document} 

I would simplify the formula first and then typeset it across three rows using an align* environment.

documentclass{article}

usepackage{amsmath}

DeclareMathOperator{E}{E}  % expectations operator



begin{document}

begin{align*}

P_t

&=frac{1}{2}(m_t+v_t-u_t)

 +frac{1}{4}frac{1-zeta}{1+zeta}

  biggl[E_{t-1}m_t +frac{1-zeta}{2zeta }E_{t-2}m_t\

&quad +frac{zeta (1-zeta)}{2(1+zeta)}E_{t-2}P_{t-1}

 +frac{zeta}{2}P_{t-1}+frac{zeta}{1+zeta }P_{t-2}

 +E_{t-2}m_t\

&quad +frac{zeta}{2} (E_{t-2}P_{t-1}+P_{t-2})biggr]

 +frac{1}{4}zeta (P_{t-1}+P_{t-2})

end{align*}

end{document}

After removing all unnecessary brackets, correcting size of used ones, with use nccmath for medium size fractions and changed lines of equation:

documentclass{article}

usepackage{nccmath}

%---------------- show page layout. don't use in a real document!

usepackage{showframe}

renewcommandShowFrameLinethickness{0.15pt}

renewcommand*ShowFrameColor{color{red}}



begin{document}

begin{multline*}

P_t=

 frac{1}{2}Biggl(m_t+v_t-u_t           \

    + frac{1-zeta }{2}frac{E_{t-1}m_t 

    + mfrac{1-zeta}{2zeta}E_{t-2}m_t

    + mfrac{zeta(1-zeta)}{2(1+zeta)}E_{t-2}P_{t-1}

    + mfrac{zeta}{2}P_{t-1} 

    + mfrac{zeta}{1+zeta}P_{t-2}}

           {1+zeta}Biggr)                \

+ frac{1-zeta}{4}

  frac{E_{t-2}m_t + frac{zeta}{2}(E_{t-2}P_{t-1} 

    + P_{t-2})}{1+zeta}  

    + frac{zeta }{4}Bigl(P_{t-1}+P_{t-2}Bigr)

end{multline*}

end{document}

(red lines indicate text borders)