3.7 Nested comprehensions
You can nest comprehensions to create lists within lists. Our task in this section is to explore several ways of making this list of four lists, each of which has four numbers:
On the left is the list of lists, and on the right is a matrix. In particular, it is a 4 by 4 identity matrix, as you see in linear algebra. The matrix is diagonal: the only non-zero entries are on the main diagonal. Coders frequently use lists of lists to implement matrices in Python.
Linear algebra is at the heart of quantum computing and many other disciplines. For now, we look at how to build the list.
In this case, it is not onerous to type in the list, but we use matrices of size 2n by 2n in quantum computing. When n is 15, we get a 32768 by 32768 matrix, for example.
Let’s begin by creating a 4 by 4 list of lists filled with zeros.
m = [[0 for i in range(4)]...
