Eli Borodach - 1 year ago 50

Python Question

Let's assume I have 2 matrices which each of them represents vector:

`X = np.matrix([[1],[2],[3]])`

Y = np.matrix([[4],[5],[6]])

I want the output to be the result of multiplying it element by element, which means it should be:

`[[4],[10],[18]]`

Notice: it is np.matrix and not np.array

10x in advance

Answer Source

so remember that NumPy matrix is a subclass of NumPy array, and array operations are element-wise.

therefore, you can convert your matrices to NumPy arrays, then multiply them with the "*" operator, which will be element-wise:

```
>>> import numpy as NP
>>> X = NP.matrix([[1],[2],[3]])
>>> Y = NP.matrix([[4],[5],[6]])
>>> X1 = NP.array(X)
>>> Y1 = NP.array(Y)
>>> XY1 = X1 * Y1
array([[ 4],
[10],
[18]])
>>> XY = matrix(XY1)
>>> XY
matrix([[ 4],
[10],
[18]])
```

alternatively you can use a generic function for element-wise multiplication:

```
>>> a = NP.matrix("4 5 7; 9 3 2; 3 9 1")
>>> b = NP.matrix("5 2 9; 8 4 2; 1 7 4")
>>> ab = NP.multiply(a, b)
>>> ab
matrix([[20, 10, 63],
[72, 12, 4],
[ 3, 63, 4]])
```

these two differ in the return type and so you probably want to choose the first if the next function in your data flow requires a NumPy array; if it requires a NumPy matrix, then the second