Odtnhj

How do i insert an underbraced under a transposed vector that spans over 2 elements in vector?

So for instance the first two elements under one underbracket with text "node 1", and ect..

the code for the vector:

documentclassstandalone
usepackageamsmath

beginequation
 mathbfD_right^T = left[ begin arraycccccccc underbrace0_textnode 1 & underbrace0_textnode 1 & underbrace0_textnode 2 & underbrace0_textnode 2 & underbrace U_x_textnode 3 & underbrace U_y_textnode 3 & underbracecos left(theta right) Delta_textnode 4 & underbracesin left(theta right) Delta_textnode 4 end array
 right]
endequation

You can do without an array here, since you're working with a single vector. Use ties (spaces, ~) to stretch out the elements:

documentclassarticle

usepackagemathtools

begindocument

beginequation
 mathbfD_mathrmright^T = 
 bigl[~
 underbracemathstrut 0 ~~~ 0_mathclaptextnode 1 ~~ 
 underbracemathstrut 0 ~~~ 0_mathclaptextnode 2 ~~ 
 underbracemathstrut U_x ~~~ U_y_textnode 3 ~~ 
 underbracecos(theta)Delta ~~~ sin(theta)Delta_textnode 4
 ~bigr]
endequation

enddocument

I'd recommend nested matrices; for the main one, use array with [t] vertical alignment.

documentclassarticle
usepackageamsmath

begindocument

beginequation
mathbfD_mathrmright^T =
Bigl[
 beginarray[t]@,cccc@,
 underbracemathstrutbeginmatrix 0 & 0 endmatrix_textnode 1 &
 underbracemathstrutbeginmatrix 0 & 0 endmatrix_textnode 2 &
 underbracemathstrutbeginmatrix U_x & U_yendmatrix_textnode 3 &
 underbracemathstrut
 beginmatrixcos(theta)Delta & sin(theta)Deltaendmatrix
 _textnode 4
 endarray
 Bigr]
endequation

enddocument

A TikZ solution, although I'm not too sure about its usefulness.

What might be advantageous of the Tikz way is the separation of vector elements and the brace markup in the source code. This might be useful when typesetting more complex / longer formulas in the cells.

However, this approach requires way more set-up than the other solutions.

documentclassscrartcl
usepackageamsmath
usepackagetikz
usetikzlibrarymatrix,decorations.pathreplacing,calc
begindocument
beginequation
 mathbfD_right^T = 
 begintikzpicture [baseline,
 underbrace/.style=decorate,thick,decoration=brace,mirror]
 matrix (eq1) [nodes=% Control for largest depth in vector
 % Change argument depth() to "deepest" node in vector
 text depth=depth("$U_y$")
 ,
 anchor=base,
 matrix of math nodes,
 left delimiter=lbrack,
 right delimiter=rbrack, 
 column sep=5mm
 ] 
 0 & 0 & 0 & 0 & U_x & U_y & cos (theta) Delta & sin (theta) Delta \; 
 % Specify braces in the format "column no where brace star/ closing column / description"
 foreach x / y / nodedesc in 1/2/node 1, 3/4/node 2, 5/6/node 3, 7/8/node 4 
 draw [underbrace] (eq1-1-x.south west) -- (eq1-1-y.south east) node [below,midway] nodedesc; 
 endtikzpicture
endequation
enddocument