[Xy-pic] brackets for one of two xymatrix diagrams in xy

[Roger Hart]

I would like to ask for some help adding brackets in xy. Within a  
single xy diagram, I've created two diagrams with xymatrix, as the  
attached PDF file shows:

The left-hand side xymatrix represents a linear algebra augmented  
matrix, and so I would like to add brackets around it, that is "["  
and "]" in the customary manner. But I need to be able to connect the  
two diagrams with arrows. I've tried several approaches, but I've run  
into four problems:

(i) While xy can draw braces  ( "{" and "}" ) and parentheses ( "("  
and ")" ), it seems that it does not draw brackets. Is this correct?

(ii) If xy cannot draw brackets, I would hope to use parentheses. But  
I have not been able to position the parentheses around the entire  
first xymatrix. How might I do this?

(iii) Related to (ii), if I try to group the xymatrix on the lhs  
using braces, I can't connect to the rhs with arrows. So I'm looking  
for a solution that will allow me to draw arrows from the xymatrix on  
the lhs to the one on the rhs.

(iv) The xy parentheses I've been able to draw are pretty thick. How  
can I make them thinner?

The xy code I'm trying to use is below (I use the package ps4pdf, but  
I've not included that code here):

		\def\determinantdiagram#1#2#3#4{%
			\xy%
			\xymatrix"*"@1@=0mm at M=0mm at R=.5mm at C=.5mm{#1}
			\POS(#2,#3)
			\xymatrix at 1@=0pt at M=0pt at R=.5mm{#4}
			\endxy}

		\determinantdiagram{
		*+<1mm>[F-:<10pt>]{k_1} \ar@/_.7pc/[ddddrrrrr] & l_1 & 0 & \cdots &  
0 & *+<1mm>[F-:<10pt>]{b_1} \\
		0 & k_2 & l_2 & \ddots & \vdots & b_2 \\
		\vdots & \ddots & \ddots & \ddots & 0 & \vdots \\
		0 & \cdots & 0 & k_{N-1} & l_{N-1} & b_{N-1} \\
		*+<1mm>[F-:<10pt>]{l_N} \ar@/^1pc/[uuuurrrrr] & -l_N l_1 & \cdots &  
-l_N l_1 \cdots l_{N-2} & k_N & *+<1mm>[F-:<10pt>]{b_N}
		}{70}{-14}{
		*+<1mm>[F-:<10pt>]{k_1 b_N}\ar@{<-}@/_7mm/["*"rrrrr]  & *+<1mm> 
[F-:<10pt>]{- l_N b_1}\ar@{<-}@/^5mm/["*"ddddrrrr]
		}

Thanks very much,

Roger

********************************

Roger Hart
Assistant Professor, Departments of History and Asian Studies
University of Texas at Austin

office: Room 470, Burdine Hall
office phone: 512-475-7258
department fax: 512-475-7222
email: rhart at mail.utexas.edu
http://uts.cc.utexas.edu/~rhart

*********************************


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