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# Authored by Weisheng Jiang
# Book 4  |  From Basic Arithmetic to Machine Learning
# Published and copyrighted by Tsinghua University Press
# Beijing, China, 2022
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# Bk4_Ch4_13.py

import numpy as np
A = np.array([[1, -1, 0], 
              [3,  2, 4],
              [-2, 0, 3]])

# calculate trace of A
tr_A = np.trace(A)