Finding Fundamental Subspaces

This example shows how to find the fundamental subspaces of the matrix


Problem

Given
Find the fundamental subspaces.

Solution

Column space :
Since , each column of is times the corresponding column of . Thus, every column of is a linear combination of the columns of , so . Moreover, because has full row rank, its rows span , meaning the columns of (as coefficients) can generate any vector in . Applying the invertible (a bijection) to the full span of yields the full . Therefore, . The columns of form a basis:

Row space :

The row space . We can then find using where:

After computing the inner product we get which we can then use to get:

Null space :

The null space satisfies To find , we need to solve Solving the linear system we get that:
This tells us that:

Null space :

We know that the null space is . Since , and we know that we know that so .