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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_a(values, n):
 """Extract the independent variables of the given values and return them as a matrix with n columns in a form suitable for the least squares approach applied in method |ARMA.update_ar_coefs|. """

        m = len(values)-n
        a = numpy.empty((m, n), dtype=float)
        for i in range(m):
            i0 = i-1 if i > 0 else None
            i1 = i+n-1
            a[i] = values[i1:i0:-1]
        return numpy.array(a)