# Matrix product (×)
	#
	# Require: `self.width == other.height`
	#
	# ~~~
	# var m = new Matrix.from([[3.0, 4.0],
	#                          [5.0, 6.0]])
	# var i = new Matrix.identity(2)
	#
	# assert m * i == m
	# assert (m * m).to_s == """
	# 29.0 36.0
	# 45.0 56.0"""
	#
	# var a = new Matrix.from([[1.0, 2.0, 3.0],
	#                          [4.0, 5.0, 6.0]])
	# var b = new Matrix.from([[1.0],
	#                          [2.0],
	#                          [3.0]])
	# var c = a * b
	# assert c.to_s == """
	# 14.0
	# 32.0"""
	# ~~~
	fun *(other: Matrix): Matrix
	do
		assert self.width == other.height

		var out = new Matrix(other.width, self.height)
		out.items.mul(items, other.items, self.width, self.height, other.width)
		return out
	end