Avoid using names like vectors and matrices when indicating numpy arrays.

Without a discussion of matrices as a 2d-array and a vector as a 1d-array in the context of general nd-arrays the language of array, matrix, and vector may be somewhat confusing. As this language is rarely used in the text it is easily avoided or clarified.

In addition, expected matrix behavior (Hadamard product versus matrix product) and the differences between the np.array and np.matrix classes may be confused here.

At line 1149 the language (N X 1) would seem to indicate a 2d column vector in the numpy notation not a 1d row vector.