**[1]** Although there is a specialized matrix data type defined in NumPy, it’s more standard to work with ordinary NumPy arrays.\n",
"See [this discussion](https://python-programming.quantecon.org/numpy.html#matrix-multiplication).\n",
"\n",
"

**[2]** Suppose that $ \\|S \\| < 1 $. Take any nonzero vector $ x $, and let $ r := \\|x\\| $. We have $ \\| Sx \\| = r \\| S (x/r) \\| \\leq r \\| S \\| < r = \\| x\\| $. Hence every point is pulled towards the origin."
]
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