(dense) matrix is:
important features:
fast access to individual items (*)
the memory, that grows like n**2
small example (double precision matrix):
>>> import numpy as np
>>> import matplotlib.pyplot as plt
>>> x = np.linspace(0, 1e6, 10)
>>> plt.plot(x, 8.0 * (x**2) / 1e6, lw=5)
[<matplotlib.lines.Line2D object at ...>]
>>> plt.xlabel('size n')
<matplotlib.text.Text object at ...>
>>> plt.ylabel('memory [MB]')
<matplotlib.text.Text object at ...>
...
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