Recursive matrix element addition for multidimensional array

Question

If the size of the matrix is (3, 4, 4);

new_matrix = matrix[0] + matrix[1] + matrix[2]

How can I do element-wise addition of each element of the matrix.'

Example:

matrix = np.array([[[1, 2], [3, 4]], [[4, 5], [6, 7]], [[8, 9], [10, 11]]])

new_matrix = np.zeros(shape=(2, 2))

for i in range(matrix.shape[0]):
    new_matrix += matrix[i]

print(new_matrix)

Answer: [[13, 16], [19, 22]]

Question: How would I do without for loop?

Sree · Accepted Answer · 2019-10-15 06:48:19Z

1

You can use np.sum function available in numpy. You can specify the axis along which you want to perform addition otherwise it will give the total sum of all elements in the matrix.

For your example,

matrix = np.array([[[1, 2], [3, 4]], [[4, 5], [6, 7]], [[8, 9], [10, 11]]])
print(np.sum(matrix,axis=0))

The output is

[[13 16]
 [19 22]]

This is the link for np.sum documentation: np.sum

answered Oct 15, 2019 at 6:48

Sree

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