[Freesurfer] How to create a 3g4v matrix

Hi Freesurfer Experts,

I’m a new user of Freesurfer, and I learn how to use this software mainly through Wiki. When I came to the step of using GLM to compare group differences, I was confused on the design of 3g4v matrix. In my study, there were 3 classes (A / B / C group) and 4 concomitant variables (gender, age, education, and Moca test score). It’s supposed to be 15 regressors in this design, but I don’t know how to use the numbers (like 1, -1, 0, 0.5, -0.5, etc.) to create a correct matrix. I wonder if you could provide a 3g4v matrix in detail for me. I’ll be grateful if you can help. I hope I’m not bothering you too much, and I’m looking for your reply. Best wishes,

Li