On Thursday, 12 November 2015 17:35:39 UTC+1, Ian wrote: > On Thu, Nov 12, 2015 at 8:57 AM, PythonDude <xxx....com> wrote: > > Hi all, > > Anyone could please explain or elaborate on exactly this (quote): "Keep in > > mind that Python has a reversed definition of rows and columns"??? > > > > That I don't understand - thank you for any > > hints/guidance/explanations/ideas/suggestions etc! > > py> import numpy > py> p = numpy.reshape(range(5), (5,1)) > py> p > array([[0], > [1], > [2], > [3], > [4]]) > py> p.T > array([[0, 1, 2, 3, 4]]) > py> p.dot(p.T) > array([[ 0, 0, 0, 0, 0], > [ 0, 1, 2, 3, 4], > [ 0, 2, 4, 6, 8], > [ 0, 3, 6, 9, 12], > [ 0, 4, 8, 12, 16]]) > py> p.T.dot(p) > array([[30]]) > py> m = numpy.asmatrix(p) > py> m > matrix([[0], > [1], > [2], > [3], > [4]]) > py> m.T > matrix([[0, 1, 2, 3, 4]]) > py> m * m.T > matrix([[ 0, 0, 0, 0, 0], > [ 0, 1, 2, 3, 4], > [ 0, 2, 4, 6, 8], > [ 0, 3, 6, 9, 12], > [ 0, 4, 8, 12, 16]]) > py> m.T * m > matrix([[30]]) > > Yeah, I don't know what that person is talking about either. It looks > correct to me.
Thank you very much, Ian - just had to be sure about this - I would also be very disappointed in Python, if this author was right about this non-intuitive interpretation of how to do matrix multiplication :-) -- https://mail.python.org/mailman/listinfo/python-list
