7.4. 对角矩阵

\[\left[ {\begin{array}{cccc} {{d_{11}}}&{}&{}&{}\\ {}&{{d_{22}}}&{}&{}\\ {}&{}& \ddots &{}\\ {}&{}&{}&{{d_{nn}}} \end{array}} \right]\left[ {\begin{array}{cccc} {{a_{11}}}&{{a_{12}}}& \cdots &{{a_{1n}}}\\ {{a_{21}}}&{{a_{22}}}& \cdots &{{a_{2n}}}\\ \vdots & \vdots & \ddots & \vdots \\ {{a_{n1}}}&{{a_{n2}}}& \cdots &{{a_{nn}}} \end{array}} \right] = \left[ {\begin{array}{cccc} {{d_{11}}{a_{11}}}&{{d_{11}}{a_{12}}}& \cdots &{{d_{11}}{a_{1n}}}\\ {{d_{22}}{a_{21}}}&{{d_{22}}{a_{22}}}& \cdots &{{d_{22}}{a_{2n}}}\\ \vdots & \vdots & \vdots & \vdots \\ {{d_{nn}}{a_{n1}}}&{{d_{nn}}{a_{n2}}}& \cdots &{{d_{nn}}{a_{nn}}} \end{array}} \right] \]