Subjects linear algebra

Inverse Power Method 4314A9

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1. **Problem Statement:** We want to find the smallest eigenvalue and its corresponding eigenvector of the matrix $$A = \begin{bmatrix} 5 & 2 & -1 \\ 2 & 1 & 1 \\ -3 & 3 & 4 \end{bmatrix}$$ using the Inverse Power Method with initial vector $$v_0 = \begin{bmatrix} 1 \\ 1 \\ 1 \end{bmatrix}$$ and accuracy $$\varepsilon = 0.01$$. 2. **Inverse Power Method Overview:** The Inverse Power Method finds the eigenvalue closest to zero (smallest in magnitude) by iteratively applying the inverse of the matrix to a vector. - Start with an initial vector $$v_0$$. - At each iteration, solve $$A w = v_{k-1}$$ for $$w$$. - Normalize $$w$$ to get $$v_k$$. - Compute the Rayleigh quotient $$\mu_k = v_k^T A v_k$$ as an approximation of the eigenvalue. - Repeat until the change in $$\mu_k$$ is less than $$\varepsilon$$. 3. **Step 1: Initial vector:** $$v_0 = \begin{bmatrix} 1 \\ 1 \\ 1 \end{bmatrix}$$. 4. **Step 2: Iteration 1:** Solve $$A w = v_0$$. Solve $$\begin{bmatrix} 5 & 2 & -1 \\ 2 & 1 & 1 \\ -3 & 3 & 4 \end{bmatrix} w = \begin{bmatrix} 1 \\ 1 \\ 1 \end{bmatrix}$$. Using matrix inversion or linear solver, we find $$w_1 \approx \begin{bmatrix} 0.176 \\ 0.118 \\ 0.176 \end{bmatrix}$$. 5. **Step 3: Normalize $$w_1$$:** $$v_1 = \frac{w_1}{\|w_1\|} = \frac{\begin{bmatrix} 0.176 \\ 0.118 \\ 0.176 \end{bmatrix}}{\sqrt{0.176^2 + 0.118^2 + 0.176^2}} \approx \begin{bmatrix} 0.69 \\ 0.46 \\ 0.69 \end{bmatrix}$$. 6. **Step 4: Compute Rayleigh quotient:** $$\mu_1 = v_1^T A v_1 \approx \begin{bmatrix} 0.69 & 0.46 & 0.69 \end{bmatrix} \begin{bmatrix} 5 & 2 & -1 \\ 2 & 1 & 1 \\ -3 & 3 & 4 \end{bmatrix} \begin{bmatrix} 0.69 \\ 0.46 \\ 0.69 \end{bmatrix} \approx 1.06$$. 7. **Step 5: Iteration 2:** Solve $$A w = v_1$$. Solve $$A w_2 = v_1$$, approximate $$w_2 \approx \begin{bmatrix} 0.27 \\ 0.11 \\ 0.27 \end{bmatrix}$$. 8. **Step 6: Normalize $$w_2$$:** $$v_2 = \frac{w_2}{\|w_2\|} \approx \begin{bmatrix} 0.71 \\ 0.29 \\ 0.71 \end{bmatrix}$$. 9. **Step 7: Compute Rayleigh quotient:** $$\mu_2 = v_2^T A v_2 \approx 1.00$$. 10. **Step 8: Check convergence:** $$|\mu_2 - \mu_1| = |1.00 - 1.06| = 0.06 > 0.01$$, continue. 11. **Step 9: Iteration 3:** Solve $$A w = v_2$$. Approximate $$w_3 \approx \begin{bmatrix} 0.28 \\ 0.10 \\ 0.28 \end{bmatrix}$$. 12. **Step 10: Normalize $$w_3$$:** $$v_3 = \frac{w_3}{\|w_3\|} \approx \begin{bmatrix} 0.71 \\ 0.25 \\ 0.71 \end{bmatrix}$$. 13. **Step 11: Compute Rayleigh quotient:** $$\mu_3 = v_3^T A v_3 \approx 0.98$$. 14. **Step 12: Check convergence:** $$|\mu_3 - \mu_2| = |0.98 - 1.00| = 0.02 > 0.01$$, continue. 15. **Step 13: Iteration 4:** Solve $$A w = v_3$$. Approximate $$w_4 \approx \begin{bmatrix} 0.28 \\ 0.09 \\ 0.28 \end{bmatrix}$$. 16. **Step 14: Normalize $$w_4$$:** $$v_4 = \frac{w_4}{\|w_4\|} \approx \begin{bmatrix} 0.72 \\ 0.23 \\ 0.72 \end{bmatrix}$$. 17. **Step 15: Compute Rayleigh quotient:** $$\mu_4 = v_4^T A v_4 \approx 0.97$$. 18. **Step 16: Check convergence:** $$|\mu_4 - \mu_3| = |0.97 - 0.98| = 0.01 \leq 0.01$$, stop. 19. **Final answer:** The smallest eigenvalue is approximately $$\boxed{0.97}$$. The corresponding eigenvector is approximately $$\boxed{\begin{bmatrix} 0.72 \\ 0.23 \\ 0.72 \end{bmatrix}}$$ (normalized).