Math Problem Statement

reverse engineer a matrix from a span of Nullspace (A) = (-2, -1, 1, 0, 0) , (-3, 2, 0, -2, 1)

Solution

To reverse engineer a matrix AA given the span of its null space, we start by recognizing that the null space vectors form a basis for the null space of AA. In other words, each of these vectors is a solution to the homogeneous system Ax=0A \mathbf{x} = 0.

The two null space vectors are:

  • v1=(2,1,1,0,0)\mathbf{v}_1 = (-2, -1, 1, 0, 0)
  • v2=(3,2,0,2,1)\mathbf{v}_2 = (-3, 2, 0, -2, 1)

These vectors tell us that: Av1=0andAv2=0A \mathbf{v}_1 = 0 \quad \text{and} \quad A \mathbf{v}_2 = 0

To reverse engineer the matrix AA, we can construct AA by creating a matrix whose rows are orthogonal to both v1\mathbf{v}_1 and v2\mathbf{v}_2. Since the null space is spanned by these two vectors, AA must have at least three rows (because the dimension of the null space is 2 and AA is underdetermined with respect to the number of constraints).

Step-by-Step Construction:

  1. Write the null space vectors as columns of a matrix:

    \begin{pmatrix} -2 & -3 \\ -1 & 2 \\ 1 & 0 \\ 0 & -2 \\ 0 & 1 \end{pmatrix}$$ This matrix $$N$$ represents the null space of the matrix $$A$$.
  2. Construct AA by finding a matrix whose row space is orthogonal to the column space of NN:

    To find AA, we need to compute a matrix AA such that Av1=0A \mathbf{v}_1 = 0 and Av2=0A \mathbf{v}_2 = 0, which means each row of AA must be orthogonal to both v1\mathbf{v}_1 and v2\mathbf{v}_2.

    We can solve for this by finding vectors orthogonal to both null space vectors.

  3. Compute the matrix AA: Let's consider the orthogonal complement of the null space. For simplicity, we assume that AA is a 3×53 \times 5 matrix (since the null space has dimension 2, the row space must have dimension 3).

    One possible matrix AA could be constructed using the row reduction process or by finding the orthogonal complement directly. Here's a potential form of the matrix:

    \begin{pmatrix} 1 & 0 & 2 & 0 & 0 \\ 0 & 1 & 1 & 0 & 0 \\ 0 & 0 & 0 & 2 & 1 \end{pmatrix}$$ This matrix has the required property that: $$A \mathbf{v}_1 = 0 \quad \text{and} \quad A \mathbf{v}_2 = 0$$

Final Answer:

The matrix AA whose null space is spanned by the vectors (2,1,1,0,0)(-2, -1, 1, 0, 0) and (3,2,0,2,1)(-3, 2, 0, -2, 1) is:

\begin{pmatrix} 1 & 0 & 2 & 0 & 0 \\ 0 & 1 & 1 & 0 & 0 \\ 0 & 0 & 0 & 2 & 1 \end{pmatrix}$$ Let me know if you need more details on this process. --- Would you like further explanation on this? Here are 5 related questions to explore: 1. What is the significance of the null space in linear algebra? 2. How do you find the orthogonal complement of a vector space? 3. What is the relationship between the rank of a matrix and the null space? 4. Can the null space determine the uniqueness of the matrix $$A$$? 5. How can the null space help in solving systems of linear equations? **Tip:** The dimension of the null space is called the "nullity" of the matrix, and it provides important information about the number of solutions to the system $$A\mathbf{x} = 0$$.

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Null Space
Matrix Construction
Orthogonality

Formulas

A * v = 0 (where v is a vector from the null space)

Theorems

Rank-Nullity Theorem
Orthogonality in Vector Spaces

Suitable Grade Level

Undergraduate Level