Proving Symmetry of (A)(A^T) Matrix w/ Tensor Notation

In summary, symmetry in a matrix refers to the property of a matrix where the elements on either side of the main diagonal are equal. To prove symmetry in a matrix, one can use the Einstein summation convention in tensor notation. It is important to prove symmetry in a matrix as it provides insights into its structure and behavior. An example of proving symmetry in a matrix using tensor notation is representing the matrix as a sum of tensor products and applying the symmetry property. Other methods for proving symmetry include using the definition of symmetry and performing row and column operations, but tensor notation is a more general and efficient method.
  • #1
neelakash
511
1

Homework Statement



We are to show that (A)(A^T) is a symmetric matrix using tensor notation.

Where ^T denotes TRANSPOSE

Homework Equations


The Attempt at a Solution



I did it in the following way:
Let P=(A)(A^T)
Then,
p_ik=(a_ij)(a_jk) Where A=a_ij and A^T=a_jk
=(a_jk^T)(a_ji)
=(a_kj)(a_ji)
=p_ki

hence proved.
Please tell if I am correct.
 
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  • #2
It seems right.
 
  • #3


Your approach seems to be correct. In tensor notation, the transpose operation can be represented by using the Kronecker delta, δ, and the Einstein summation convention. So, your calculation can be written as:

p_ik = a_ij a_jk = a_ij δ_jk = a_jk δ_ji = a_kj δ_ij = a_ki = p_ki

Which shows that the components of the matrix P are symmetric, thus proving that P is a symmetric matrix.
 

1. What is the definition of symmetry in a matrix?

Symmetry in a matrix refers to the property of a matrix where the elements on either side of the main diagonal are equal. In other words, the matrix is symmetric if it is equal to its transpose.

2. How do you prove the symmetry of a matrix using tensor notation?

To prove symmetry in a matrix using tensor notation, we can use the Einstein summation convention. This involves rewriting the matrix as a sum of tensor products and then applying the symmetry property of tensors.

3. Why is it important to prove symmetry in a matrix?

Proving symmetry in a matrix is important because it is a fundamental property that can provide insights into the structure and behavior of the matrix. It is also used in various applications, such as in physics and engineering.

4. Can you provide an example of proving symmetry in a matrix using tensor notation?

Yes, for example, if we have a matrix A = [[1, 2], [2, 3]], we can represent it as a tensor A = Aijei⊗ej where ei and ej are basis vectors. Using the symmetry property of tensors, we can rewrite A as A = 0.5(A + AT)⊗(ei⊗ej + ej⊗ei). Since A = AT, we can conclude that A is symmetric.

5. Are there any other methods to prove symmetry in a matrix?

Yes, there are other methods such as using the definition of symmetry, where we check if the elements on either side of the main diagonal are equal. Another method is to perform row and column operations to see if the resulting matrix is equal to its transpose. However, using tensor notation is a more general and efficient method for proving symmetry in a matrix.

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