# Matrices

A DataFrame is generally composed of rows, and each row has the same number of columns. From one point of view, it's a two-dimensional grid containing lots of numbers. It can also be interpreted as a list of lists, or an array of arrays.

In mathematics, a matrix is a rectangular array of numbers defined by the number of rows and columns. It is standard always to list rows first, and columns second. For instance, a 2 x 3 matrix consists of 2 rows and 3 columns, whereas a 3 x 2 matrix consists of 3 rows and 2 columns.

Here is a 4 x 4 matrix:

## Exercise 132: Matrices

NumPy has methods for creating matrices or n-dimensional arrays. One option is to place random numbers between 0 and 1 into each entry, as follows.

In this exercise, you will implement the various `numpy`

matrix methods and observe the outputs (recall that `random.seed`

will allow us to reproduce the same numbers, and it&apos...