When the model does not contain more than 25 parts, this window lets you choose which Parts you want to interact by checking boxes in a matrix.
When a model contains more than 25 parts, the matrix option is not available and will be greyed-out.
If you have a large number of Parts, you may find it easy to set interactions using the Add / Remove options in the Interactions dialog panel.
The matrix shown in this panel lists the Parts of your model vertically and horizontally. This matrix is symmetrical, so only the diagonal and lower part of the matrix is shown.
Check a box if you want the two associated Parts to interact.
The Remove buttons let you quickly uncheck the boxes for each row of the matrix.
Click to apply the changes you make to the matrix.