matlab operations of 2 numpy arrays of same shape in python

Question

I have 2 numpy array with equal shape.

V = [[-1 -1 -1] [-2 -2 -2] [-3 -3 -3]]
U = [[1 2 3] [2 3 4] [3 4 5]]

I want to convert matlab to python for below line.

Ot = U*([V(:,1) V(:,2) -V(:,3)])';

I want to convert this matlab code in python.
How can I do that? Inside V(:,1) and V(:,2) are multiplying?

You yourself have asked multiplying arrays previously: stackoverflow.com/questions/21179499/… — zhangxaochen
– zhangxaochen, Commented Jan 17, 2014 at 9:48

zhangxaochen · Accepted Answer · 2014-01-17 10:06:38Z

1

It's not multiplying V(:,1) by V(:,2), it's just separating them by white space. code [V(:,1) V(:,2) -V(:,3)] in matlab just generates matrix:

>> [V(:,1) V(:,2) -V(:,3)]

ans =

    -1    -1     1
    -2    -2     2
    -3    -3     3

so the equivalent could be:

In [90]: V = np.array([[-1, -1, -1], [-2, -2, -2], [-3, -3, -3]])
    ...: U = np.array([[1, 2, 3], [2, 3, 4], [3, 4, 5]])

In [91]: V[:, 2]*=-1

In [92]: Ot = U.dot(V.T)

In [93]: Ot
Out[93]: 
array([[ 0,  0,  0],
       [-1, -2, -3],
       [-2, -4, -6]])

edited Jan 17, 2014 at 10:06

answered Jan 17, 2014 at 9:58

zhangxaochen

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