I have 2 numpy arrays
[a] = [[1] [2] [3]]
[b] = [[4] [5] [6]]
I want to convert matlab line to python
A = a*b';
How I will do this in python and what ' signifies in matlab?
2 Answers
use numpy.dot:
In [7]: a=np.array([1,2,3])
In [8]: b=np.array([4,5,6,])
In [9]: a.dot(b)
Out[9]: 32
if you want the result still be a matrix, use numpy.matrix:
In [239]: ma=matrix([1,2,3])
In [240]: ma
Out[240]: matrix([[1, 2, 3]])
In [241]: mb=matrix([4,5,6])
In [242]: mb.T
Out[242]:
matrix([[4],
[5],
[6]])
In [243]: ma*mb.T
Out[243]: matrix([[32]])
update:
If your arrays are 2D arrays, which are of shape (m, n) when you print a.shape, you should transpose the second array using .T, otherwise you get ValueError: objects are not aligned:
In [30]: a
Out[30]: array([[1, 2, 3]])
In [31]: b
Out[31]: array([[4, 5, 6]])
In [32]: a.dot(b.T)
Out[32]: array([[32]])
In [33]: a.dot(b)
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-33-9a1f5761fa9d> in <module>()
----> 1 a.dot(b)
ValueError: objects are not aligned
Comments
you need transpose the first array:
import numpy as np
a = np.array([[1], [2], [3]])
b = np.array([[4], [5], [6]])
np.dot(a.T, b)
or the second array:
np.dot(a, b.T)
'operator is the transpose operator in MATLAB. See mathworks.com/help/dsp/ref/transpose.html