Display Mathematica Matrices in 2D Format

As noted in the documentation (http://support.wolfram.com/kb/28318), versions of Mathematica from 11.1x and later allow matrix output to be changed via the Option Inspector. The steps are presented below.

Change the Default Type of New Cells - Windows

1. Launch Mathematica and make sure a notebook is open.
2. On the Mathematica main menu, select Edit > Preferences...
3. Click on the Advanced tab.
4. Click on the Open Option Inspector button.
5. In the left frame, select Cell Options > New Cell Defaults > CommonDefaultFormatTypes.
6. To the left of the word "Output", click in the margin and you should see an X appear.
7. To the right of the word "Output", double-click on the words StandardForm and replace them with the words TraditionalForm.
8. Press the Enter key.
9. Click on the Apply button near the top middle of the dialog box.
10. Close all open dialog boxes. This change should now be permanent in future sessions for the current user.

Change the Default Type of New Cells - Mac

1. Launch Mathematica.
2. On the Mathematica main menu, select Mathematica > Preferences...
3. Click on the Advanced tab.
4. Click on the Open Option Inspector button.
5. In the Options column, open Cell Options > New Cell Defaults > CommonDefaultFormatTypes.
6. Within the CommonDefaultFormatTypes folder, find the word "Output." Click to the far left of the word "Output" (near the left edge of the dialog box in the Set column) and you should see an X appear.
7. To the right of the word "Output", double-click on the words StandardForm and replace them with the words TraditionalForm 
8. Press the enter key.
9. Close all open dialog boxes. This change should now be permanent in future sessions for the current user.