Hi,
On Mon, Jan 5, 2015 at 8:40 PM, Colin J. Williams <cjwilliam...@gmail.com> wrote: > One of the essential characteristics of a matrix is that it be rectangular. > > This is neither spelt out or checked currently. > > The Doc description refers to a class: > > - *class *numpy.matrix[source] > > <http://github.com/numpy/numpy/blob/v1.9.1/numpy/matrixlib/defmatrix.py#L206> > > Returns a matrix from an array-like object, or from a string of data. A > matrix is a specialized 2-D array that retains its 2-D > nature through operations. It has certain special operators, such as * > (matrix multiplication) and ** (matrix power). > > This illustrates a failure, which is reported later in the calculation: > > A2= np.matrix([[1, 2, -2], [-3, -1, 4], [4, 2 -6]]) > > Here 2 - 6 is treated as an expression. > FWIW, here A2 is definitely rectangular, with shape== (1, 3) and dtype== object, i.e elements are just python lists. > Wikipedia offers: > > In mathematics <http://en.wikipedia.org/wiki/Mathematics>, a *matrix* > (plural *matrices*) is a rectangular > <http://en.wikipedia.org/wiki/Rectangle> *array > <http://en.wiktionary.org/wiki/array>*[1] > <http://en.wikipedia.org/wiki/Matrix_%28mathematics%29#cite_note-1> of > numbers <http://en.wikipedia.org/wiki/Number>, symbols > <http://en.wikipedia.org/wiki/Symbol_%28formal%29>, or expressions > <http://en.wikipedia.org/wiki/Expression_%28mathematics%29>, arranged in *rows > <http://en.wiktionary.org/wiki/row>* and *columns > <http://en.wiktionary.org/wiki/column>*.[2] > <http://en.wikipedia.org/wiki/Matrix_%28mathematics%29#cite_note-2>[3] > <http://en.wikipedia.org/wiki/Matrix_%28mathematics%29#cite_note-3> > (and in this context also python objects). -eat > The individual items in a matrix are called its *elements* or *entries*. > An example of a matrix with 2 rows and 3 columns is > [image: \begin{bmatrix}1 & 9 & -13 \\20 & 5 & -6 \end{bmatrix}.]In the > Numpy context, the symbols or expressions need to be evaluable. > > Colin W. > > > > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > >
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