The author needs to be careful in what model they are using to show asymptotic runtime. Sure, this reduces to O(log n) matrix multiplications, but matrix multi

The author needs to be careful in what model they are using to show asymptotic runtime. Sure, this reduces to O(log n) matrix multiplications, but matrix multiplication is not a constant time operation (and is actually between quadratic/cubic in the dimension of the matrix, assuming arithmetic operations are performed in constant time, which is also not always a great assumption).