don't understand matrix-multiplication should be reversed in python?

[Dave Farrance]

PythonDude <mjoerg.phone at gmail.com> wrote:

>On Thursday, 12 November 2015 22:57:21 UTC+1, Robert Kern  wrote:

>> He simply instantiated the two vectors as row-vectors instead of column-vectors, 
>> which he could have easily done, so he had to flip the matrix expression.
>
>Thank you very much Robert - I just had to be sure about it :-)

Yep, he's evidently used to the Matlab/Octave way of defining "vectors"
which is somewhat easier for a math-oriented interactive environment.

It's just a *bit* more laborious to append columns in numpy.

>>> from numpy import *
>>> v1=vstack([0,1,2])
>>> v2=vstack([3,4,5])
>>> c_[v1,v2]
array([[0, 3],
       [1, 4],
       [2, 5]])
>>> append(v1,v2,axis=1)
array([[0, 3],
       [1, 4],
       [2, 5]])
>>> v3=mat('4;5;6')
>>> v4=mat('7;8;9')
>>> c_[v3,v4]
matrix([[4, 7],
        [5, 8],
        [6, 9]])