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Boxing Multiple Lines in Split

TeX - LaTeX Asked by Jaredan Durbin on April 17, 2021

I want to put a box around the final two lines in this

begin{equation}
begin{split}
leftlanglevec{u}rightrangle&=frac{1}{4}Releft(epsilon_0vec{overset{sim}{E}}cdotvec{overset{sim}{E}}^*+frac{1}{mu_0}vec{overset{sim}{B}}cdotvec{overset{sim}{B}}^*right) 
&=frac{1}{4}left[epsilon_0left(frac{piomega B_0}{left(frac{omega}{c}right)^2-k^2}right)^2left[left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)+left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]right. 
&qquad+frac{1}{mu_0}left(frac{pi kB_0}{left(frac{omega}{c}right)^2-k^2}right)^2left[left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)+left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)right. 
&qquadqquadleft.left(frac{left(frac{omega}{c}right)^2-k^2}{pi k}right)cos^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right] 

%Box starting here

&=left(frac{pi B_0}{2left[left(frac{omega}{c}right)^2-k^2right]}right)^2left[left(epsilon_0omega+frac{k}{mu_0}right)left[left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)right.right. 
&qquadleft.left.+left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]+left(frac{left(frac{omega}{c}right)^2-k^2}{pimu_0k}right)cos^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]

%and ending here

end{split}
end{equation}

First block of code output
I want it to pretty much look like this

begin{equation}
begin{split}
leftlanglevec{S}rightrangle&=frac{1}{2mu_0}Releft(vec{overset{sim}{E}}timesvec{overset{sim}{B}}^*right) 
&=frac{1}{2mu_0}Releft(frac{ipi B_0}{left(frac{omega}{c}right)^2-k^2}left[leftlanglefrac{-nomega}{b}left[cosleft(frac{mpi}{a}xright)sinleft(frac{npi}{b}yright)right],frac{momega}{a}left[sinleft(frac{mpi}{a}xright)cosleft(frac{npi}{b}yright)right],0rightrangleright.right. 
&qquadtimesleftlanglefrac{mk}{a}left[sinleft(frac{mpi}{a}xright)cosleft(frac{npi}{b}yright)right],frac{nk}{b}left[cosleft(frac{mpi}{a}xright)sinleft(frac{npi}{b}yright)right],right. 
&qquadqquadleft.left.left.frac{-ileft[left(frac{omega}{c}right)^2-k^2right]}{pi}cosleft(frac{mpi}{a}xright)cosleft(frac{npi}{b}yright)rightrangleright]right) 
&=frac{1}{2mu_0}Releft(frac{ipi B_0}{left(frac{omega}{c}right)^2-k^2}leftlanglefrac{-imomegaleft[left(frac{omega}{c}right)^2-k^2right]}{pi a}sinleft(frac{mpi}{a}xright)cosleft(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright),right.right. 
&qquadfrac{inomegaleft[left(frac{omega}{c}right)^2-k^2right]}{pi b}cos^2left(frac{mpi}{a}xright)sinleft(frac{npi}{b}yright)cosleft(frac{npi}{b}yright), frac{-n^2omega k}{b^2}left[cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)right] 
&qquadqquadleft.left.-frac{m^2omega k}{a^2}left[sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]rightrangleright) 
&fbox{$=frac{omega B_0}{2mu_0}leftlanglefrac{m}{a}sinleft(frac{mpi}{a}xright)cosleft(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright),frac{n}{b}cos^2left(frac{mpi}{a}xright)sinleft(frac{npi}{b}yright)cosleft(frac{npi}{b}yright),0rightrangle$}
end{split}
end{equation}

Second block of code output
I’ve tried using fbox, but I cannot seem to get it to span multiple lines keeping my paragraphing and tabs. Also sorry for the messy code!

2 Answers

The amsmath package provides a macro called boxed for just this purposes. Note that I encased an aligned environment inside the boxed directive. And I also replaced all instances of left(frac{omega}{c}right) with (omega/c) to achieve a more compact appearance of the formulas.

In the following solution, the = symbol is not inside the box. If it has to be inside the box, you'll need to replace

%Box starting here
&=boxed{begin{aligned}[t]
&biggl(frac{pi B_0}{2left[(omega/c)^2-k^2right]}biggr)^{!2}

with

%Box starting here
&boxed{begin{aligned}
&=biggl(frac{pi B_0}{2left[(omega/c)^2-k^2right]}biggr)^{!2}

in the code given below.

enter image description here

documentclass{article}
usepackage[letterpaper,margin=1in]{geometry} % set page parameters appropriately
usepackage{amsmath}
usepackage{mleftright} % for tightly-spaced left...right constructs
mleftright

begin{document}
begin{equation}
begin{split}
langlevec{u}mkern1.5murangle
&=frac{1}{4}ReBigl( epsilon_0vec{widetilde{E}}cdotvec{widetilde{E}}^*
 +frac{1}{mu_0}vec{widetilde{B}}cdotvec{widetilde{B}}^* Bigr) 
&=frac{1}{4}
 Biggl[
 epsilon_0
 left(frac{piomega B_0}{(omega/c)^2-k^2}right)^{!2}
 left[left(frac{n}{b}right)^2cos^2
 left(frac{mpi}{a}xright)sin^2
 left(frac{npi}{b}yright)
+left(frac{m}{a}right)^2sin^2
 left(frac{mpi}{a}xright)cos^2
 left(frac{npi}{b}yright)right] 
&qquad+frac{1}{mu_0}
 left(frac{pi kB_0}{(omega/c)^2-k^2}right)^{!2}
 left[left(frac{m}{a}right)^2sin^2
 left(frac{mpi}{a}xright)cos^2
 left(frac{npi}{b}yright)
+left(frac{n}{b}right)^2cos^2
 left(frac{mpi}{a}xright)sin^2
 left(frac{npi}{b}yright)right. 
&qquadqquad
 left(frac{(omega/c)^2-k^2}{pi k}right)cos^2 
 left(frac{mpi}{a}xright)cos^2
 left(frac{npi}{b}yright) 
 Biggr] 
%Box starting here
&=boxed{begin{aligned}[t]
&biggl(frac{pi B_0}{2left[(omega/c)^2-k^2right]}biggr)^{!2}
 Biggl[
 left(epsilon_0omega+frac{k}{mu_0}right)
 biggl[left(frac{n}{b}right)^2cos^2
 left(frac{mpi}{a}xright)sin^2
 left(frac{npi}{b}yright) 
&qquad+left(frac{m}{a}right)^2sin^2
 left(frac{mpi}{a}xright)cos^2
 left(frac{npi}{b}yright)biggr]
+left(frac{(omega/c)^2-k^2}{pimu_0k}right)cos^2
 left(frac{mpi}{a}xright)cos^2
 left(frac{npi}{b}yright)
 Biggr] 
end{aligned}}
%and ending here
end{split}
end{equation}
end{document}

Correct answer by Mico on April 17, 2021

The Aboxed command from mathtools alows for including the alignment point in a framebox. To enclose several lines I use the multlined environment from the same package, and aligned for the lines above:

documentclass{article}
usepackage{geometry} 
usepackage{mathtools}

begin{document}

begin{equation}
begin{split}
leftlanglevec{u}rightrangle&=frac{1}{4}Releft(epsilon_0vec{overset{sim}{E}}cdotvec{overset{sim}{E}}^*+frac{1}{mu_0}vec{overset{sim}{B}}cdotvec{overset{sim}{B}}^*right) 
&=begin{alignedat}[t]{2} frac{1}{4}Biggl[& epsilon_0left(frac{piomega B_0}{left(frac{omega}{c}right)^2-k^2}right)^{mkern-5mu 2} left[left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)+left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right] & & 
 & +frac{1}{mu_0}left(frac{pi kB_0}{left(frac{omega}{c}right)^2 - k^2}right)^{mkern-5mu 2} biggl[left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)%
 & & mathllap{+left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)
left(frac{left(frac{omega}{c}right)^2-k^2}{pi k}right)cos^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)Biggr]} &
end{alignedat}
%Box starting here
Aboxed{&=begin{multlined}[t] left(frac{pi B_0}{2left[left(frac{omega}{c}right)^2-k^2right]}right)^{mkern-5mu 2} left[left(epsilon_0omega+frac{k}{mu_0}right)left[left(frac{n}{b}right)^2cos^2left(frac{mpi}{a}xright)sin^2left(frac{npi}{b}yright)right.right. 
left.left.+left(frac{m}{a}right)^2sin^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]+left(frac{left(frac{omega}{c}right)^2-k^2}{pimu_0k}right)cos^2left(frac{mpi}{a}xright)cos^2left(frac{npi}{b}yright)right]
end{multlined}}
%and ending here
end{split}
end{equation}

 end{document} 

enter image description here

Answered by Bernard on April 17, 2021

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