Nullspace and Column Space Question

In summary, the nullspace of a subspace W is equal to the rowspace of its orthogonal complement V. This can be proven by showing that a vector x is in the nullspace of A if and only if it is orthogonal to all the rows of A. Therefore, the nullspace of A is the orthogonal complement of the rowspace of A.
  • #1
Bouchart
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Nullspace and Orthogonal Complement

Quick question: is the nullspace the orthogonal complement of the column space or the the row space?

Thanks, sorry I don't have my textbook nearby.
 
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  • #2
Hey that was just in my linear algebra exam the other day. The theorem goes:
nullspace[W]=rowspace[V]

where W is the subspace and V is the orthogonal complement
 
  • #3
I never memorize these things. Especially when they are quite easy to reproduce.
A vector x is in the nullspace of A iff Ax=0.
The components of Ax are the dot products of the row vectors of A with x. All the components must be zero, so x is in the nullspace of A iff it is orthogonal to all the rows of A.
Therefore the the nullspace of A the is orthogonal complement of the rowspace of A.
 

1. What is nullspace and column space?

Nullspace and column space are concepts used in linear algebra to describe the set of vectors that satisfy certain conditions. The nullspace, also known as the kernel, is the set of all vectors that produce a zero output when multiplied by a given matrix. The column space, also known as the range, is the set of all possible linear combinations of the columns of a given matrix.

2. How are nullspace and column space related to each other?

Nullspace and column space are closely related as they are both used to describe the properties of a matrix. The nullspace is the orthogonal complement of the column space, meaning that any vector in the nullspace is perpendicular to every vector in the column space. This relationship is known as the fundamental theorem of linear algebra.

3. What is the significance of nullspace and column space?

Nullspace and column space are important concepts in linear algebra as they allow us to understand the properties and behavior of a matrix. They can be used to determine the rank and nullity of a matrix, and to solve systems of linear equations. Additionally, the column space is used in applications such as data compression and image recognition.

4. How can I find the nullspace and column space of a matrix?

To find the nullspace of a matrix, you can use Gaussian elimination to put the matrix in reduced row-echelon form. The columns corresponding to the pivot variables will form a basis for the column space, while the columns corresponding to the non-pivot variables will form a basis for the nullspace. Alternatively, you can use the singular value decomposition (SVD) method to find the nullspace and column space of a matrix.

5. What are some real-world applications of nullspace and column space?

Nullspace and column space have many practical applications in fields such as engineering, computer science, and economics. They are used in data analysis, image processing, and optimization problems. In engineering, they are used to model physical systems and solve complex equations. In computer science, they are used in machine learning algorithms and data compression techniques. In economics, they are used in game theory and market analysis.

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