NumPy: numpy.asmatrix() function

numpy.asmatrix() function

The numpy.asmatrix() function is used to interpret the input as a matrix.
Unlike matrix, asmatrix does not make a copy if the input is already a matrix or an ndarray. Equivalent to matrix(data, copy=False).

Syntax:

numpy.asmatrix(data, dtype=None)

Parameters:

Return value:

mat : matrix
data interpreted as a matrix.

Example: Converting ndarray to matrix with asmatrix()

>>> import numpy as np
>>> x = np.array([[1,2], [3,4]])
>>> n = np.asmatrix(x)
>>> x[0,0] = 5
>>> n
matrix([[5, 2],
        [3, 4]])

The above code demonstrates the use of asmatrix() function to convert an ndarray to a matrix. Initially, an ndarray x with values [[1,2],[3,4]] is created. Using asmatrix() function, x is converted to a matrix n.
The two-dimensional matrix n is a view of the array x. Then the value of x[0,0] is changed to 5. Since both x and n share the same data buffer, the change in value of x is reflected in n. Therefore, n now becomes [[5,2],[3,4]].

Pictorial Presentation:

Example-2: NumPy.asmatrix() function

>>> import numpy as np
>>> a = np.array([[2,3], [4,5]])
>>> x = np.asmatrix(a)
>>> a[0,0] = 5
>>> x
matrix([[5, 3],
        [4, 5]])

Pictorial Presentation:

Python - NumPy Code Editor:

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