2-dimensional numpy

Question 1

Cast a list to an array

Answer 1

A = np.array(a)
A
array([[11, 12, 13],
       [21, 22, 23],
       [31, 32, 33]])

Question 2

ndim

Answer 2

obtain the number of axes or dimensions referred to as the rank.
a.ndim
2

Question 3

shape

Answer 3

returns a tuple corresponding to the size or number of each dimension.
A.shape
(3, 3)
go down vertical first and horizontal second

Or total number of nested list first, the number of elements in each nested list second

Question 4

size

Answer 4

The total number of elements in the array
A.size
9

Question 5

Obtain elements

Answer 5

A[0:2, 2]
array([13, 23])

you first go down the vertical axis along 0:2 before you go across along 2

Question 6

Matrix multiplcation using *

Answer 6

Multiplication of two arrays corresponds to an element-wise product or Hadamard product. Consider matrix X and Y. The Hadamard product corresponds to multiplying each of the elements in the same position, i.e. multiplying elements contained in the same color boxes together. The result is a new matrix that is the same size as matrix Y or X, as shown in the following figure.

Question 7

get transorse

Answer 7

C.T
array([[1, 2, 3],
[1, 2, 3]])