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Prove the following statement:

If A∈Cᵐˣⁿ,m≥n,rank(A)=n, then the reduced non-negative QR factorization is unique.

Hints:
1. Consider the uniqueness of the nonnegative Cholesky factorization (Theorem 3.5.15) of AᴴA, including the explanation of why it exists for AᴴA.
2. Substitute the QR factorization into AHA and compare it to the Cholesky factorization.

1 Answer

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The statement "if a = m * n, then the reduced non-negative np factorization is unique" is true.

The following statement is true: if a = m * n, then the reduced non-negative np factorization is unique.

Proof:

Suppose that a = m * n = p * q, where m, n, p, and q are all positive integers. Then, we can write:

m * n = p * q

Dividing both sides by mn, we get:

1 = p / m * q / n

This implies that p / m and q / n are both rational numbers.

Since m and n are coprime, p and q must also be coprime.

Since p / m and q / n are both rational numbers, we can write them as p / m = a / b and q / n = c / d, where a, b, c, and d are all positive integers. Then, we can write:

p = am and q = cn

Substituting these values into the equation a = m * n, we get:

am * cn = m * n

Canceling common factors, we get:

ac = 1

This implies that a and c must be equal to 1 or -1. Since a and c are both positive integers, they must be equal to 1.

Therefore, p = m and q = n, and the reduced non-negative np factorization of a is unique.

Example: Consider the integer a = 12. The prime factorization of 12 is 2^2 * 3. The reduced non-negative np factorization of 12 is (2, 2) * (3, 1).

Now, suppose that a = 12 = 4 * 3. The prime factorization of 4 * 3 is also 2^2 * 3.

The reduced non-negative np factorization of 4 * 3 is also (2, 2) * (3, 1).Therefore, the reduced non-negative np factorization of 12 is unique.

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