Rank of a 4x4 Matrix A: Linear Algebra Homework Solution

In summary, the rank of A is 3, which is equal to both the column rank and the row rank. This means that there are three linearly independent rows in the matrix, and the remaining vectors are also linearly independent. To ensure accuracy, one can check this by looking at the row reduction of the matrix.
  • #1
underacheiver
12
0

Homework Statement


Find the rank of A =
{[1 0 2 0]
[4 0 3 0]
[5 0 -1 0]
[2 -3 1 1]}

Homework Equations





The Attempt at a Solution


i row reduced A to be:
{[1 0 0 0]
[0 1 0 -1/3]
[0 0 1 0]}

where do i go from here?
 
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  • #2
I think you omitted a last row of zeros. Ok, what does rank mean?
 
  • #3
The column rank of a matrix A is the maximal number of linearly independent columns of A. Likewise, the row rank is the maximal number of linearly independent rows of A.

Since the column rank and the row rank are always equal, they are simply called the rank of A.
 
  • #4
underacheiver said:
The column rank of a matrix A is the maximal number of linearly independent columns of A. Likewise, the row rank is the maximal number of linearly independent rows of A.

Since the column rank and the row rank are always equal, they are simply called the rank of A.

Good! So how many linearly independent rows are there? If you have no idea, quote the definition of linear independence.
 
  • #5
so is it 3? because the 2nd and 4th columns are dependent.
 
  • #6
underacheiver said:
so is it 3? because the 2nd and 4th columns are dependent.

Yes, the second and fourth columns being dependent means the rank is at most 3. Now you have to check that the three remaining vectors are linearly independent. It's easier to see this if you look at the row reduction.
 

1. What is the rank of a matrix in linear algebra?

The rank of a matrix is the maximum number of linearly independent rows or columns in the matrix. It is a measure of the dimension or "size" of the vector space spanned by the rows or columns of the matrix.

2. How is the rank of a matrix determined?

The rank of a matrix can be determined by performing row reduction operations on the matrix and counting the number of non-zero rows or columns in the reduced matrix. Alternatively, it can also be determined by finding the number of pivot columns in the matrix after performing Gaussian elimination.

3. What is the significance of the rank of a matrix?

The rank of a matrix is important because it tells us how many linearly independent rows or columns exist in the matrix. It also determines the dimension of the vector space spanned by the rows or columns of the matrix, which can have implications in applications such as data analysis and machine learning.

4. Can the rank of a matrix change?

Yes, the rank of a matrix can change if the matrix undergoes a linear transformation. However, the rank of a matrix is an inherent property and does not change based on row or column operations.

5. How does the rank of a matrix relate to its inverse?

A square matrix is invertible if and only if its rank is equal to its dimension. This means that a matrix with full rank (rank equal to its dimension) will have an inverse, while a matrix with less than full rank will not have an inverse.

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