NumPy 练习题 003

ID：

21. Create a checkerboard 8x8 matrix using the tile function
    ```python
    ```
22. Normalize a 5x5 random matrix
    ```python
    ```
23. Create a custom dtype that describes a color as four unsigned bytes (RGBA)
    ```python
    ```
24. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product)
    ```python
    ```
25. Given a 1D array, negate all elements which are between 3 and 8, in place. 
    ```python
    ```
26. What is the output of the following script?
    ```python
    # Author: Jake VanderPlas

    print(sum(range(5),-1))
    from numpy import *
    print(sum(range(5),-1))
    ```
    ```python
    ```    
27. Consider an integer vector Z, which of these expressions are legal?
    ```python3
    Z**Z
    2 << Z >> 2
    Z <- Z
    1j*Z
    Z/1/1
    Z<Z>Z
    ```
    ```python
    ```   
28. What are the result of the following expressions?
    ```python
    np.array(0) / np.array(0)
    np.array(0) // np.array(0)
    np.array([np.nan]).astype(int).astype(float)
    ```
    ```python
    ```    
29. How to round away from zero a float array ? 
    ```python
    ```
30. How to find common values between two arrays?
    ```python
    ```