QBUS1040 Tutorial 7 Semester 2, 2022
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QBUS1040
Tutorial 7
Semester 2, 2022
Exercise 1: Block matrix notation Consider the block matrix A = lB(I)T 「 0 |
B 0 0 |
0(0) 」 BBT |
where B is 10 × 5. What are the dimensions of the five zero matrices and the identity matrix in the definition of A? What are the dimensions of A?
Exercise 2: Interpolation of rational functions
A rational function of degree two has the form
c1 + c2 t + c3 t2
f(t) =
where c1 ,c2 ,c3 ,d1 ,d2 are coefficients. Consider the interpolation conditions
f(ti ) = yi , i = 1, . . . ,K,
where ti and yi are given numbers. Express the interpolation conditions as a set of linear equations in the vector of coefficients θ = (c1 ,c2 ,c3 ,d1 ,d2 ), as Aθ = b. Give A and b and their dimensions.
Exercise 3: Required nutrients
We consider a set of n basic foods (such as rice, beans, apples) and a set of m nutrients or components (such as protein, fat, sugar, vitamin C). Food j has a cost given by cj (say, in dollars per gram), and contains an amount Nij of nutrient i (per gram). (The nutrients are given in some appropriate units, which can depend on the particular nutrient.) A daily diet is represented by an n-vector d, with di the daily intake (in grams) of food i. Express the condition that a diet d contains the total nutrient amounts given by the m-vector ndes , and has a total cost B (the budget) as a set of linear equations in the variables d1 , ...,dn . (The entries of d must be non-negative, but we ignore this issue here.)
Exercise 4: QR factorization using Gram-Schmidt algorithm: Code it up!
Perform QR factorization on a random matrix A with Gram-Schmidt algorithm using Python. Verify that QT Q = I and R is upper triangular with positive diagonal entries. Simulate a larger random matrix A and time your QR factorization.
2022-09-20