Python NumPy3 Selections

Question 1

How do you create a matrix?

Answer 1

Create a list of lists, then convert using the numpy array function

Question 2

How do you do matrix multiplication?

Answer 2

With the dot function

Question 3

How do you invert a matrix

Answer 3

With the np.linalg.inv function

Question 4

How can you compute eigenvalues and eigenvectors?

Answer 4

Using the np.linalg.eig method

Question 5

How would you select a single value from a NumPy array?

Answer 5

Use indexing, for example V[0] or V[5]

Question 6

How can you extract a range of values?

Answer 6

By slicing, for example, V[2:5] and you can do stuff like this: V[:2] and V[2:]

Question 7

How can you set a selection of values in an array equal to a constant?

Answer 7

By “broadcasting” for example,
V[4:6] = 33 remember these intervals are half open, like this: [,)

Question 8

Value assignment propagates

Answer 8

Like this

Question 9

How can you prevent propagation?

Answer 9

By using copy.

Question 10

How to select a value from a matrix

Answer 10

There are two syntaxes that would work. Both use brackets.

Question 11

How to select a submatrix?

Answer 11

Do slicing with the colon.

Question 12

Vector operation. How to perform a simple test on every element of an array?

Answer 12

Just apply it to the object name

Question 13

How can you use that boolean as a selector?

Answer 13

Pop it into brackets. Or even do this: V[V>24]