如何在 python 中乘以负幂的数字

Question

When I try to multiply this by a negative integer it just returns an error

I use:

A = np.array([[1,2,0], [2,4,-2], [0,-2,3]])

Answer 1

From the screenshot, I can see this is homework.

So it asks for the matrix inverse. In maths this is written as A^(-1)

import numpy as np

A = np.array([[1,2,0], [2,4,-2], [0,-2,3]])
np.linalg.inv(A)

array([[-2.  ,  1.5 ,  1.  ],
       [ 1.5 , -0.75, -0.5 ],
       [ 1.  , -0.5 ,  0.  ]])

Answer 2

In numpy, you can not raise integers by negative integer powers (Read this ).

In python, the ** operator returns the value without any error.

In [6]: A = 20                                                                                                                                                                          

In [7]: print(A ** -1)                                                                                                                                                                  
0.05

You can also use pow() ,

In [1]: A = 20

In [2]: pow(20, -1)
Out[2]: 0.05

Answer 3

If you're working with matrices, it's a good idea to ensure that they are instances of the numpy.matrix type rather than the more-generic numpy.ndarray .

import numpy as np
M = np.matrix([[ ... ]])

To convert an existing generic array to a matrix you can also pass it into np.asmatrix() .

Once you have a matrix instance M , one way to get the inverse is MI

To avoid the "integers not allowed" problem, ensure that the dtype of your matrix is floating-point, not integer (specify dtype=float in the call to matrix() or asmatrix() )

Answer 4

To Insert power as negative value assume an another variable and name it "pow" and assign that negative value. Now put below in your code.

pow = -3
value = 5**pow
print(value)

Execute the code and you will see result. Hope it helps...