Matrices

[komame]

The problem arises from the fact that you used the M1 variable, which is a built-in global variable for HOME (not CAS), and it only stores numerical values in matrices. Create your own variable, e.g. "mat1" (preferably in lowercase, as is customary in CAS, though uppercase would also work) and do the same thing, and you'll see there won't be an issue. Alternatively, you can perform the calculations directly without using variables.