Error in multline

Question

This is related to my early question, but with some changes:

\documentclass[11pt,twoside,a4paper]{article}
\usepackage{amsmath}
\usepackage{enumerate}
 \begin{document}
  \begin{multline}
 E(y_{i})=
\left(
 x_{2i}'\beta_{2}+
\frac{\sigma}{\Psi\left(x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho\right)}
\left[
\phi\left(\tfrac{x_{2i}'\beta_{2}}{\sigma}\right)\Phi\left(\tfrac{x_{1i}'\beta_{1}-   \rho\tfrac{x_{2i}'\beta_{2}}{\sigma}}{\left(1-\rho^{2}\right)^{1/2}}\right)\right.\\
\qquad 
+ \left. 
\rho\phi(x_{1i}'\beta_{1})\Phi\left(\tfrac{\tfrac{x_{2i}'\beta_{2}}{\sigma}-\rho x_{1i}'\beta_{1}}{\left(1-\rho^{2}\right)^{1/2}}\right)
\right]
\right)
\times\Psi\left(x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho
\right)
\end{multline} 
\end{document}

I have no idea why this is generating an error. !Missing right \.inserted

Answer 1

If you really had to use \left and \right... Additional ones marked.

\documentclass[11pt,twoside,a4paper]{article}
\usepackage{amsmath}
\usepackage{enumerate}
 \begin{document}
  \begin{multline}
 E(y_{i})=
\left(
 x_{2i}'\beta_{2}+
\frac{\sigma}{\Psi\left(
x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho
\right)}
\left[
\phi\left(
\tfrac{x_{2i}'\beta_{2}}{\sigma}
\right)\Phi\left(
\tfrac{x_{1i}'\beta_{1}-   \rho\tfrac{x_{2i}'\beta_{2}}{\sigma}}{\left(1-\rho^{2}\right)^{1/2}}
\right)
\right.
\right. % PS
\\
\qquad 
+ \left. 
\left. %PS
\rho\phi(x_{1i}'\beta_{1})\Phi\left(
\tfrac{\tfrac{x_{2i}'\beta_{2}}{\sigma}-\rho x_{1i}'\beta_{1}}{\left(1-\rho^{2}\right)^{1/2}}
\right)
\right]
\right)
\times\Psi\left(
x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho
\right)
\end{multline} 
\end{document}

Answer 2

You'd got one left/right pair mis-matched but using \left( zzz\right. is not optimal anyway as the matching brackets will not be given the same size as the open is sized on the expression before \\ and the close is sized on the expression after \\. Using fixed size delimiters makes it easier to avoid the error and produces matching delimiters:

\documentclass[11pt,twoside,a4paper]{article}
\usepackage{amsmath}
\usepackage{enumerate}
\begin{document}
  \begin{multline}
 E(y_{i})=
\Bigl(
\bigl(
 x_{2i}'\beta_{2}+
\frac{\sigma}{\Psi (x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho)}
\bigl[
\phi(\tfrac{x_{2i}'\beta_{2}}{\sigma})\Phi (\tfrac{x_{1i}'\beta_{1}-   \rho\tfrac{x_{2i}'\beta_{2}}{\sigma}}{(1-\rho^{2})^{1/2}})\\
\qquad 
+  
\rho\phi(x_{1i}'\beta_{1})\Phi(\tfrac{\tfrac{x_{2i}'\beta_{2}}{\sigma}-\rho x_{1i}'\beta_{1}}{(1-\rho^{2})^{1/2}})
\bigr]
\bigr)
\times\Psi(x_{1i}'\beta_{1},\tfrac{x_{2i}'\beta_{2}}{\sigma},\rho)
\Bigr)
\end{multline} 
\end{document}

Answer 3

Just for completion, know that you can avoid \left[ \right] by using \Big[ \Big] or \Bigg[ \Bigg] to manually get the desired size of brackets.