How to align multiple eqnarrays?

Question

I tried to created 2 eqnarrays but the equations in those 2 eqnarrays don't line up together. Here is the code:

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{txfonts}
\begin{document}
\begin{eqnarray}
\label{eq1}
&& diag\frac{\partial P}{\partial \theta}= 
diag(-diag(V)[Gdiag(V)\sin(Abus)^{T}-Bdiag(V)cos(Abus)^{T}]
\nonumber\\
&& -diag(V).^{2}diag(diag(B))))  \\
\label{eq2}
&& nondiag\frac{\partial P}{\partial \theta}= 
VV^{T}.* G .* \sin(Abus) -VV^{T}.*B .* \cos(Abus)   
\end{eqnarray}
Replace the diagnol elements of the (\ref{eq2}) with the elements of the                
(\ref{eq1}), we will get the complete $\partial P/\partial \theta$
\begin{eqnarray}
\label{eq3}
&& diag\frac{\partial P}{\partial V}=
diag(Gdiag(V)\cos(Abus)^{T}+Bdiag(V)sin(Abus)^{T}
\nonumber\\
&& +diag(V)diag(diag(G))))  \\
\label{eq4}
&& nondiag\frac{\partial P}{\partial V}= 
diag(V)G .* \cos(Abus) + diag(V)B .* \sin(Abus)   
\end{eqnarray}
Replace the diagnol elements of the (\ref{eq4}) with the elements of the    
(\ref{eq3}), we will get the complete $\partial P/\partial V$
\end{document}

And the result is: We can see that the start positions of equation (1),(2) and equation (3),(4) are different. How can I solve this problem? Thank you.

What does the operator .* do? Is it even an operator? Similarly, what does .^{2} do? — Mico, Apr 28 '15 at 07:59
.* means it's not matrix multiplication, but element multiplication. For two 22 matrix A and B, the result C would be a 22 matrix with C(1,1)=a11b11,C(1,2)=a12b12,C(2,1)=a21b21,C(2,2)=a22b22 — user3391299, Apr 28 '15 at 11:35

Ignasi · Accepted Answer · 2015-04-28T08:05:42.137

Replacing eqnarray by align the result is not perfectly aligned, but I looks like it is and I think nicer than with eqnarray.

Following Ian's suggestion diag and nondiag are declared math operators. Also parenthesis sizes has been adjusted.

After Mico's comment a new command dotstar has been declared. It's not clear for me what it does.

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{txfonts}

\DeclareMathOperator{\diag}{diag}
\DeclareMathOperator{\nondiag}{nondiag}
\newcommand\dotstar{\mathbin{.*}}

\begin{document}
\begin{align}
\label{eq1}
\diag\frac{\partial P}{\partial \theta} & = 
\diag\left(-\diag(V)\left[Gdiag(V)\sin(Abus)^{T}-B\diag(V)cos(Abus)^{T}\right]\right.
\nonumber\\
&\quad \left.-\diag(V).^{2}\diag\left(\diag(B)\right)\right)  \\
\label{eq2}
\nondiag\frac{\partial P}{\partial \theta} & = 
VV^{T}\dotstar G\dotstar\sin(Abus)-VV^{T}\dotstar B\dotstar\cos(Abus)   
\end{align}
Replace the diagnol elements of the (\ref{eq2}) with the elements of the                
(\ref{eq1}), we will get the complete $\partial P/\partial \theta$
\begin{align}
\label{eq3}
\diag\frac{\partial P}{\partial V} & =
\diag\left(G\diag(V)\cos(Abus)^{T}+B\diag(V)sin(Abus)^{T}\right.
\nonumber\\
&\quad +\Bigl.\diag(V)\diag\left(\diag(G)\right)\Bigr)  \\
\label{eq4}
\nondiag\frac{\partial P}{\partial V}&= 
\diag(V)G\dotstar\cos(Abus) + \diag(V)B\dotstar\sin(Abus)   
\end{align}
Replace the diagnol elements of the (\ref{eq4}) with the elements of the    
(\ref{eq3}), we will get the complete $\partial P/\partial V$
\end{document}

enter image description here

But if you want all equations perfectly aligned, insert the middle paragraph inside a \intertext command.

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{txfonts}

\DeclareMathOperator{\diag}{diag}
\DeclareMathOperator{\nondiag}{nondiag}
\newcommand\dotstar{\mathbin{.*}}

\begin{document}
\begin{align}
\label{eq1}
\diag\frac{\partial P}{\partial \theta} & = 
\diag\left(-\diag(V)\left[Gdiag(V)\sin(Abus)^{T}-B\diag(V)cos(Abus)^{T}\right]\right.
\nonumber\\
&\quad \left.-\diag(V).^{2}\diag\left(\diag(B)\right)\right)  \\
\label{eq2}
\nondiag\frac{\partial P}{\partial \theta} & = 
VV^{T}\dotstar G\dotstar\sin(Abus)-VV^{T}\dotstar B\dotstar\cos(Abus)   
%\end{align}
\intertext{Replace the diagnol elements of the (\ref{eq2}) with the elements of the                
(\ref{eq1}), we will get the complete $\partial P/\partial \theta$}
%\begin{align}
\label{eq3}
\diag\frac{\partial P}{\partial V} & =
\diag\left(G\diag(V)\cos(Abus)^{T}+B\diag(V)sin(Abus)^{T}\right.
\nonumber\\
&\quad +\Bigl.\diag(V)\diag\left(\diag(G)\right)\Bigr)  \\
\label{eq4}
\nondiag\frac{\partial P}{\partial V}&= 
\diag(V)G\dotstar\cos(Abus) + \diag(V)B\dotstar\sin(Abus)   
\end{align}
Replace the diagnol elements of the (\ref{eq4}) with the elements of the    
(\ref{eq3}), we will get the complete $\partial P/\partial V$
\end{document}

enter image description here

I think you should also use \DeclareMathOperator for diag and nondiag. — Ian Thompson, Apr 28 '15 at 07:09
@Mico I don't know what .* means. Which refinement do you suggest? — Ignasi, Apr 28 '15 at 07:36
I'm not sure either what .* does, but I assume it's some kind of operator of type mathbin. Thus, I'd define the macro \dotstar iia \newcommand\dotstar{\mathbin{.*}} in the preamble and write \dotstar in the equations themselves. Probably not perfect, but almost certainly better than what's produced by writing .* directly. — Mico, Apr 28 '15 at 07:48
@Mico I've applied your suggestion while waiting for OP's answer. Thank you. — Ignasi, Apr 28 '15 at 08:06
@Mico@IanThompson Thank you. The operator I mean it's not matrix multiplication, but element multiplication. For two 22 matrix A and B, the result C would be a 22 matrix with C(1,1)=a11b11,C(1,2)=a12b12,C(2,1)=a21b21,C(2,2)=a22b22. I hope you understand what I mean. — user3391299, Apr 28 '15 at 11:43
@user3391299 Looks like a Hadamard product which I didn't know until now. In this case, you can replace \dotstar with \circ. — Ignasi, Apr 28 '15 at 12:08
I'm not sure you want to have fleqn that changes all displayed equations just for aligning some of them. — egreg, Apr 28 '15 at 12:30
@egreg I've just copied fleqn from OP's code, I don't know what it does and don't remember to have ever used it. — Ignasi, Apr 28 '15 at 12:53

score 2 · Answer 2 · edited Apr 13 '17 at 12:35

Never use eqnarray (see eqnarray vs align)

Here the combination of align with split seems the best way to tackle the problem.

\documentclass{article}
\usepackage{mathtools}
\usepackage{newtxtext,newtxmath}

\DeclareMathOperator{\diag}{diag}
\DeclareMathOperator{\nondiag}{nondiag}
\newcommand{\dotstar}{\mathbin{.{*}}}
\newcommand{\Abus}{\mathit{Abus}}

\begin{document}

\begin{align}
\begin{split}
\diag\frac{\partial P}{\partial \theta} & = 
\diag\bigl(-\diag(V)[G \diag(V)\sin(\Abus)^{T}-B\diag(V)\cos(\Abus)^{T}]\\
&\qquad -\diag(V)^{2}\diag(\diag(B))\bigr)
\end{split}
\label{eq1} \\
\nondiag\frac{\partial P}{\partial \theta} & = 
VV^{T}\dotstar G\dotstar \sin(\Abus)-VV^{T}\dotstar B\cos(\Abus)   
\label{eq2}\\
\intertext{%
  By replacing the diagonal elements of the (\ref{eq2}) with the elements of
  equation~\eqref{eq1}, we will get the complete $\partial P/\partial \theta$}
\begin{split}
\diag\frac{\partial P}{\partial V} & =
  \diag\bigl(G\diag(V)\cos(\Abus)^{T}+B\diag(V)\sin(\Abus)^{T} \\
&\qquad +\diag(V)\diag(\diag(G))\bigr)
\end{split}
\label{eq3}\\
\nondiag\frac{\partial P}{\partial V}&= 
\diag(V)G\dotstar \cos(\Abus) + \diag(V)B\dotstar \sin(\Abus)   
\label{eq4}
\end{align}
By replacing the diagonal elements of equation~\eqref{eq4} with the elements of
equation~\eqref{eq3}, we will get the complete $\partial P/\partial V$

\end{document}

I replaced txfonts with newtxtext and newtxmath (the fonts for math are better and the packages are actively maintained).

If you add the tbtags option to amsmath the equation number will be aligned with the bottom line of the split parts.

I removed all \left and \right that served no purpose whatsoever (they just added unwanted horizontal space). Just a couple of \big pairs are needed.

enter image description here

how come there's not a \big on the outer parens in the first equation? (those parens are outside \big pair of brackets, and the outer parens are \big in equation (3).) — barbara beeton, Apr 28 '15 at 12:36

score 0 · Answer 3 · answered Apr 28 '15 at 07:09

Using intertext in one align environment gets the alignment:

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{txfonts}
\begin{document}
\begin{align}
\label{eq1}
& diag\frac{\partial P}{\partial \theta}= 
diag(-diag(V)[Gdiag(V)\sin(Abus)^{T}-Bdiag(V)cos(Abus)^{T}]
\nonumber\\
& -diag(V).^{2}diag(diag(B))))  \\
\label{eq2}
& nondiag\frac{\partial P}{\partial \theta}= 
VV^{T}.* G .* \sin(Abus) -VV^{T}.*B .* \cos(Abus)   
\intertext{Replace the diagnol elements of the (\ref{eq2}) with the     elements of the                
(\ref{eq1}), we will get the complete $\partial P/\partial \theta$}
\label{eq3}
&diag\frac{\partial P}{\partial V}=
diag(Gdiag(V)\cos(Abus)^{T}+Bdiag(V)sin(Abus)^{T}
   \nonumber\\
& +diag(V)diag(diag(G))))  \\
\label{eq4}
  & nondiag\frac{\partial P}{\partial V}= 
   diag(V)G .* \cos(Abus) + diag(V)B .* \sin(Abus)   
 \end{align}
    Replace the diagnol elements of the (\ref{eq4}) with the elements        of    the    
(\ref{eq3}), we will get the complete $\partial P/\partial V$
\end{document}

How to align multiple eqnarrays?

3 Answers3