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I wish to create a matrix with an non-standard type of square bracket around it. The vertical part of the left and right brackets needs to consist of two parallel line segments slightly separated. The short horizontal line segments at the top and bottom of a bracket (the segments which make the bracket "square") are not doubled, unlike the vertical part of the bracket.

I can get the effect by using two expandable square brackets with negative spaces between them, but it doesn't look good. Depending on the size of the matrix, I have to adjust the number of negative spaces by trial and error.I have seen this sort of bracket around matrices in Leo Dorst's *Geometric Algebra for Computer Science* (Elsevier, 2007).I use version 5.0 of Scientific WorkPlace.

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## I looked at the example you

I looked at the example you mentioned (See www.amazon.com/Geometric-Algebra-Computer-Science-Revised/dp/0123749425) and I think the author used consecutive brackets on each side of the matrix. If the spacing problem you mentioned arises from the number of rows you have in the matrix, you could define fragments for the row heights you need. In addition, examine the package stmaryrd.sty. (See texdoc.net/texmf-dist/doc/fonts/stmaryrd/stmaryrd.pdf)

## I'm not sure exactly what you

I'm not sure exactly what you want. See if using a matrix with delimiters that is then surrounded by expanding brackets will work. I couldn't find any discussion of what you want by searching the news group comp.text.tex via Google (http://groups.google.com/group/comp.text.tex/topics).