Math Problem Statement

Let A be a square matrix that is filled with all zeros except for the coordinates where the row number equals the column number. In those cells, the numbers from 1 to n appear in alphabetical order based on each number’s English spelling. For example if n=3 then the order would be 1-3-2. Find the trace of A**2

Solution

To solve the problem, let's break it down step by step:

Step 1: Understand the matrix AA

  • AA is a square matrix of size n×nn \times n.
  • All off-diagonal elements are zeros, i.e., AA is a diagonal matrix.
  • The diagonal entries of AA are not in the natural order 1,2,3,,n1, 2, 3, \dots, n; instead, they are arranged based on the alphabetical order of the numbers written in English.

Step 2: Diagonal ordering for n=3n=3

For n=3n=3, the numbers 1, 2, and 3, in English, are:

  • 1: "one"
  • 2: "two"
  • 3: "three"

The alphabetical order of these is:

  1. "one" (1)
  2. "three" (3)
  3. "two" (2)

Thus, the diagonal of matrix AA is [1,3,2][1, 3, 2].

Step 3: Matrix A2A^2

Since AA is a diagonal matrix, squaring it is straightforward. When squaring a diagonal matrix, you square each diagonal element individually. Hence, the diagonal of A2A^2 will be: A2=diag(12,32,22)=diag(1,9,4)A^2 = \text{diag}(1^2, 3^2, 2^2) = \text{diag}(1, 9, 4)

Step 4: Trace of A2A^2

The trace of a matrix is the sum of its diagonal elements. So, for matrix A2A^2: Trace(A2)=1+9+4=14\text{Trace}(A^2) = 1 + 9 + 4 = 14

Conclusion

The trace of A2A^2 is 14\boxed{14}.


Would you like more details on the properties of diagonal matrices or any specific part of this solution?

Here are some related questions to further your understanding:

  1. What is the trace of a matrix and why is it important?
  2. How does the alphabetical ordering affect the arrangement of numbers in a matrix?
  3. What happens to the trace if the matrix was not diagonal?
  4. How would you generalize the approach for larger values of nn?
  5. Can you think of a way to programmatically find the alphabetical order of numbers for any nn?

Tip: When squaring a diagonal matrix, remember that the off-diagonal elements remain zero, and only the diagonal elements are squared.

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Matrix Operations
Diagonal Matrix
Trace of a Matrix

Formulas

Trace(A) = sum of diagonal elements
Matrix squaring: A^2 = A * A for diagonal matrices

Theorems

Properties of Diagonal Matrices
Trace Theorem

Suitable Grade Level

Undergraduate Mathematics