https://machinelearningmastery.com/gentle-introduction-n-dimensional-arrays-python-numpy/
https://docs.scipy.org/doc/numpy-1.13.0/user/quickstart.html
http://www.scipy-lectures.org/intro/numpy/operations.html
https://www.tutorialspoint.com/numpy/numpy_indexing_and_slicing.htm
https://docs.scipy.org/doc/numpy-1.13.0/reference/arrays.indexing.html
http://www.scipy-lectures.org/intro/numpy/array_object.html
    a[from-idx:to-idx]
    a[from-idx:]
    a[:to-idx]
    a = np.arange(15) -> [0, 1, ..., 14]
        a[2:13] - trim first and last 2 items
https://pythonworld.ru/numpy/1.html

a=[2, 4, 7, 10]
for p in [0, 25, 33, 50, 66, 75, 100]:
    print numpy.percentile(a, p, interpolation='linear')

a = np.random.randn(10, 5)
    10 vectors, 5 elements each