The Windows menu contains an item "Matrix Panel...". Choosing this item will open a panel allowing easy creation of matrices. Only a small space is provided for each matrix entry, but larger items can be edited elsewhere and pasted into the matrix. This wonderful panel is the work of Jonas Zimmermann, who can be reached at zimmerleut@gmx.de.

In TeXShop 1.35, the Matrix Panel can also create tables. This panel can be configured using the file "matrixpanel_1.plist" in ~/Library/TeXShop/MatrixPanel. The structure of this file was revised in 1.35; an old "matrixpanel.plist" file may remain from TeXShop 1.34.

There is a hidden preference item to set the default size of matrices created by the panel. To change the default

  defaults write TeXShop matrixsize 12

Basic Help
Matrix Panel