2. Consider the left shift map L ∶ FN Ð→ FN given by L((an)) = (an+1), that isL(a1, a2, a3, . . . ) = (a2, a3, . . . ).(a) Prove that L is a surjective linear map. What is the kernel of L?(b) Prove that for all p ⩾ 1 and for p = ∞, the restriction of L to ℓp is a surjective continuousmap onto ℓp.(c) Define the right shift map R ∶ FN Ð→ FN and prove that it is an injective linear map,the restriction of which is distance-preserving for any ℓp with p ⩾ 1 and p = ∞.(d) Check that L ○ R = idFN ≠ R ○ L
Question
- Consider the left shift map L ∶ FN Ð→ FN given by L((an)) = (an+1), that isL(a1, a2, a3, . . . ) = (a2, a3, . . . ).(a) Prove that L is a surjective linear map. What is the kernel of L?(b) Prove that for all p ⩾ 1 and for p = ∞, the restriction of L to ℓp is a surjective continuousmap onto ℓp.(c) Define the right shift map R ∶ FN Ð→ FN and prove that it is an injective linear map,the restriction of which is distance-preserving for any ℓp with p ⩾ 1 and p = ∞.(d) Check that L ○ R = idFN ≠ R ○ L
Solution
(a) To prove that L is a surjective linear map, we need to show that for every sequence b in FN, there exists a sequence a in FN such that L(a) = b. Let b = (b1, b2, b3, ...). We can define a = (0, b1, b2, b3, ...) such that L(a) = b. This shows that L is surjective.
The kernel of L is the set of all sequences a in FN such that L(a) = 0. In this case, it is the set of all sequences that start with 0, i.e., a = (0, a2, a3, ...).
(b) To prove that the restriction of L to ℓp is a surjective continuous map onto ℓp, we need to show that for every sequence b in ℓp, there exists a sequence a in ℓp such that L(a) = b, and that the map L is continuous. The surjectivity can be shown in the same way as in part (a). The continuity of L can be shown by noting that for any two sequences a and b in ℓp, the distance between L(a) and L(b) is less than or equal to the distance between a and b, which is the definition of a continuous map.
(c) The right shift map R is defined by R((an)) = (0, a1, a2, ...). To prove that it is an injective linear map, we need to show that if R(a) = R(b), then a = b. If R(a) = R(b), then (0, a1, a2, ...) = (0, b1, b2, ...), which implies that a = b. Therefore, R is injective. The restriction of R to any ℓp is distance-preserving because the distance between R(a) and R(b) is equal to the distance between a and b.
(d) L ○ R is the identity map on FN because for any sequence a in FN, L(R(a)) = a. However, R ○ L is not the identity map on FN because for any sequence a in FN, R(L(a)) = (0, a1, a2, ...) ≠ a.
Similar Questions
1. Consider the map π1 ∶ FN Ð→ F given byπ1((an)) = a1.(a) Show that π1 is linear.(b) Prove that the restriction of π1 to ℓ∞ or to ℓp for p ⩾ 1 is continuous and surjective
1. Consider the map π1 ∶ FN Ð→ F given byπ1((an)) = a1.(a) Show that π1 is linear
Which of the following is/are true? (A) Every linear transformation from R 2 to R 2 maps lines onto points or lines (B) Every surjective linear transformation from R 2 to R 2 maps lines onto lines (C) Every bijective linear transformation from R 2 to R 2 maps pairs of parallel lines to pairs of parallel lines (D) Every bijective linear transformation from R 2 to R 2 maps pairs of perpendicular lines to pairs of perpendicular lines
(b) Assume that {v1, v2, · · · , vk} is a basis of Y . Show that the linear transform T : X → Y from (a) is invertible. (Hint: Use (a) to define a suitable linear transform U : Y → X and show that it is the inverse of T .)
This problem provides a useful way to construct invertible linear maps between subspaces X ⊂ Rn and Y ⊂ Rm.3 Let B = {u1, u2, · · · , uk} be a basis of X. (a) Let {v1, v2, · · · , vk} ⊂ Y . Show that there exists a unique linear transform T : X → Y such that T(uj) = vj for every 1 ≤ j ≤ k. To be specific, you need to 1) define a function4 T : X → Y and verify that it is linear, 2) show that if T0 : X → Y is a linear map such that T0(uj) = vj, then T = T0.
Upgrade your grade with Knowee
Get personalized homework help. Review tough concepts in more detail, or go deeper into your topic by exploring other relevant questions.