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Linear Algebra, Theory And Applications, 2012a

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496 ANSWERS TO SELECTED EXERCISES<br />

G.20 Exercises<br />

G.23 Exercises<br />

12.9<br />

1 volume is √ 218<br />

3 0.<br />

G.21 Exercises<br />

13.12<br />

13 This is easy because you show it preserves distances.<br />

15 (Ax, x) =(UDU ∗ x, x) =(DU ∗ x,U ∗ x) ≥ δ 2 |U ∗ x| 2 =<br />

δ 2 |x| 2<br />

16 0 > ((A + A ∗ ) x, x) =(Ax, x)+(A ∗ x, x)<br />

=(Ax, x) +(Ax, x) NowletAx = λx. Then you<br />

get 0 >λ|x| 2 + ¯λ |x| 2 =Re(λ) |x| 2<br />

19 If Ax = λx, then you can take the norm of both<br />

sides and conclude that |λ| =1. It follows that the<br />

eigenvalues of A are e iθ ,e −iθ and another one which<br />

has magnitude 1 and is real. This can only be 1 or<br />

−1. Since the determinant is given to be 1, it follows<br />

that it is 1. Therefore, there exists an eigenvector<br />

for the eigenvalue 1.<br />

G.22 Exercises<br />

14.7<br />

⎛<br />

1 ⎝ 0.09 ⎞<br />

0.21 ⎠<br />

0.43<br />

⎛<br />

⎞<br />

4. 237 3 × 10−2<br />

3 ⎝ 7. 627 1 × 10 −2 ⎠<br />

0.711 86<br />

28 You have H = U ∗ DU where U is unitary and D is<br />

a real diagonal matrix. Then you have<br />

⎛<br />

⎞<br />

∑<br />

∞<br />

e iH = U ∗ (iD) n<br />

e iλ1<br />

U = U ∗ ⎜<br />

⎝<br />

. ..<br />

⎟<br />

⎠ U<br />

n!<br />

e iλn<br />

n=0<br />

and this is clearly unitary because each matrix in<br />

the product is.<br />

15.3<br />

1<br />

2<br />

3<br />

4<br />

⎛<br />

⎝ 1 2 3<br />

⎞<br />

2 2 1.0 ⎠, eigenvectors:<br />

3 1 4<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.534 91 ⎬<br />

⎝ 0.390 22 ⎠ ↔ 6. 662,<br />

⎩<br />

⎭<br />

0.749 4<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.130 16 ⎬<br />

⎝ 0.838 32 ⎠ ↔ 1. 679 0,<br />

⎩<br />

⎭<br />

−0.529 42<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.834 83 ⎬<br />

⎝ −0.380 73 ⎠ ↔−1. 341<br />

⎩<br />

⎭<br />

−0.397 63<br />

⎛<br />

⎝ 3 2 1.0 ⎞<br />

2 1 3 ⎠, eigenvectors:<br />

1 3 2<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.577 35 ⎬<br />

⎝ 0.577 35 ⎠<br />

⎩<br />

⎭ ↔ 6.0,<br />

0.577 35<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.788 68 ⎬<br />

⎝ −0.211 32 ⎠ ↔ 1. 732 1,<br />

⎩<br />

⎭<br />

−0.577 35<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.211 32 ⎬<br />

⎝ −0.788 68 ⎠ ↔−1. 732 1<br />

⎩<br />

⎭<br />

0.577 35<br />

⎛<br />

⎝ 3 2 1.0 ⎞<br />

2 5 3 ⎠, eigenvectors:<br />

1 3 2<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.416 01 ⎬<br />

⎝ 0.779 18 ⎠ ↔ 7. 873 0,<br />

⎩<br />

⎭<br />

0.468 85<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.904 53 ⎬<br />

⎝ −0.301 51 ⎠<br />

⎩<br />

⎭ ↔ 2.0,<br />

−0.301 51<br />

⎧⎛<br />

⎞⎫<br />

⎨ 9. 356 8 × 10−2 ⎬<br />

⎝ −0.549 52 ⎠ ↔ 0.127 02<br />

⎩<br />

⎭<br />

0.830 22<br />

⎛<br />

⎝ 0 2 1.0 ⎞<br />

2 5 3 ⎠, eigenvectors:<br />

1 3 2<br />

⎧⎛<br />

⎞⎫<br />

⎨ 0.284 33 ⎬<br />

⎝ 0.819 59 ⎠ ↔ 7. 514 6,<br />

⎩<br />

⎭<br />

0.497 43

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