How to get a 5 x 5 matrix

Hi I am doing a shockwave simulator based on Eulers equations of gas. The solver I’m using uses matrices, the standard functionality of the fmatrix is what i need, however for 3 dimensions i require a 5 x 5 matrix. I’m going to try extending fmatrix, but if this problem has occured before I’d love to hear what soloutions were most effective.