[calvo_machine_learn] Replace np.sum(a * b) with a @ b#214

mmcky merged 2 commits intoQuantEcon:mainQuantEcon/lecture-python-advanced.myst:mainfrom

suda-yuga:calvo_machine_learn_npsumsuda-yuga/lecture-python-advanced.myst:calvo_machine_learn_npsumCopy head branch name to clipboard