If you have a number of large matrices, and you wish to determine whether each matrix has determinant zero or not, what is the most efficient way to do this in MAGMA

(it appears that calculating the rank is slightly more efficient than calculating the determinant).

**EDIT: **In case it helps, the matrix entries are rational functions in two commuting variables, which come from the coefficients of a power series in a third, noncommuting variable: the aim is to get some sort of indication of when a power series represents a rational function, which requires checking the determinant of progressively larger matrices until it starts being zero. (Although the overall setting is noncommutative, everything in the matrices themselves is commutative so there's no need to worry about left/right determinants, quasi-determinants, etc.)