A diagonal matrix and its associated quadratic form

Define a diagonal matrix:

D:= {\bf diag}(1,4,-3) =\left(\begin{array}{ccc} 1 & 0 & 0 \\ 0 & 4 & 0 \\ 0 & 0 & -3 \end{array}\right).

For the matrix above, the associated quadratic form is

q(x) = x^T\left(\begin{array}{ccc} 1 & 0 & 0 \\ 0 & 4 & 0 \\ 0 & 0 & -3 \end{array}\right) x = x_1^2 +4x_2^2 - 3x_3^2.

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Hyper-Textbook: Optimization Models and Applications Copyright © by L. El Ghaoui. All Rights Reserved.

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