For the board stiffness data discussed in Example 14.3.3, obtain the covariance matrix and then using the cov2cor function, obtain the correlation matrix.

Data from in Example 14.3.3

Four measures of stiffness of 30 boards are available. The first measure of stiffness is obtained by sending a shock wave down the board, the second measure is obtained by vibrating the board, and the remaining are obtained from static tests. We see that the mean, variance-covariance matrix, as well as the correlation matrix are very easy to compute.

The matrix of scatter plots indicate that there might be an outlier among the observations. We will say more about this in the coming subsection.

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> data (stiff) > mean (stiff) x1 x2 x3 x2 1906.100 1749.533 1509.133 1724.967 > var (stiff) x1 x4 x3 x4 x1 105616.30 94613.53 87289.71 94230.73 x2 94613.53 101510.12 76137.10 81064.36 x3 87289.71 76137.10 91917.09 90352.38 x4 94230.73 81064.36 90352.38 104227.96 > cor (stiff)