Math 170A Assignment #1
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Math 170A Assignment #1
Due date and time: 11pm, August 13, 2023 (PDT)
1. Compute the matrix power A5 for the matrix
Show all the computational results for A2, A3 , A4 .
2. Let A = [a1 a2] be a m-by-2 matrix. If X = [x21(x11) x22(x12)], find an
explicit expression for the matrix product AX in terms of a1 , a2 and xij .
3. Find all matrices A ∈ R2×2 such that the matrix equation AX = 0 has an invertible matrix solution X ∈ R2×2 .
4. For A ∈ Rn×n , if the equation Ax = bhas a solution for every b ∈ Rn , show that A is invertible.
5. Consider the following lower triangular system
Solve this system by column-oriented forward substitution.
6. Decide the range for the value of t such that the following matrix is positive definite.
7. For A e Rn×n and X e Rn ×m , if A is positive definite and X has the rankm, show that the matrix product XTAX is also positive definite.
8. Let A = [A21(A11) A22(A12)] be a 2 × 2 block matrix, for submatrices A11 e
Rn1×n1 , A12 e Rn1×n2 , A21 e Rn2×n1 , A22 e Rn2×n2 . If A is posi- tive definite, show that A11 is invertible and the matrix B := A22 一 A21A11(-)1 A12 is also positive definite.
9. Let A = [0 A22(A11 A12)] be a 2 × 2 block matrix, for submatrices A11 e
Rn1×n1 , A12 e Rn1×n2 , A22 e Rn2×n2 . The 0 is a zero matrix of dimension n2 × n1 . Suppose A11, A22 are invertible. Show that A is invertible and A-1 is a 2 × 2 block matrix of the form
[0(X)11 X22(X12)] .
Express Xij in terms of A11, A12 , A22 .
10. Consider the linear system Ax = b, with
Find a unit lower triangular matrix L and an upper triangular matrix U such that A = LU. Find vectors x,y such that Ly = b and Ux = y.
2023-09-15