Question 1. Consider a p-dimensional response variable j, containing p variables, with n observation vectors j1, ..., Tn. The sample mean vecior of these observation vectors is denoted by j = (1/n) E, Ji. a) Given that the sample covariance matrix, S, is defined by n (5i – 5) (5. – 5)", S 1=1 i) Show that E – njj

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Chapter2: Second-order Linear Odes
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Question 1. Consider a p-dimensional response variable j, containing p variables, with n observation
vectors j1, ..., n. The sample mean vector of these observation vectors is denoted by = (1/n)E1 Fi.
a) Given that the sample covariance matrix, S, is defined by
n
1
(5i – 5) (7. – 5)" ,
S
-
1=1
i) Show that
S =
i=1
ii) Using the above result, show that S can alternatively be defined as
s=" (1-) .
yT
Y,
n -
where Y is the data matrix, I is the identity matrix and J is a matrix of 1's.
[Hint: Consider re-writing the mean vector g in terms of the data matrix (see lecture notes).
b) Consider the following (3x3) data matrix, containing three observations of three variables y1, y2 and y3:
5 2 2
1 3 5
6 4 1
Y =
Calculate
i) The sample covariance matrix S (by hand);
ii) The sample correlation matrix R (by hand) using the equation
R= D,-SD,-',
and comment on each of the three elements in the first column of this matrix.
[Hint: Recall how to find the inverse of a diagonal matrix.]
Transcribed Image Text:Question 1. Consider a p-dimensional response variable j, containing p variables, with n observation vectors j1, ..., n. The sample mean vector of these observation vectors is denoted by = (1/n)E1 Fi. a) Given that the sample covariance matrix, S, is defined by n 1 (5i – 5) (7. – 5)" , S - 1=1 i) Show that S = i=1 ii) Using the above result, show that S can alternatively be defined as s=" (1-) . yT Y, n - where Y is the data matrix, I is the identity matrix and J is a matrix of 1's. [Hint: Consider re-writing the mean vector g in terms of the data matrix (see lecture notes). b) Consider the following (3x3) data matrix, containing three observations of three variables y1, y2 and y3: 5 2 2 1 3 5 6 4 1 Y = Calculate i) The sample covariance matrix S (by hand); ii) The sample correlation matrix R (by hand) using the equation R= D,-SD,-', and comment on each of the three elements in the first column of this matrix. [Hint: Recall how to find the inverse of a diagonal matrix.]
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