Using of matrices in simulink block diagrams
If you want to build a block that has matrix operations there are to blocks that will let you do this, the Fcn block and the MATLAB function block, you can



You can carry through matrices with signals as shown below. The example shows a 1x3 vector multiplied by itself and displayed in the scope as a 3x3 matrix.

Care must be taken to ensure size is preserved for the matrix operation



But the math you have shown above does not make sense, as you should either be creating two states (for example \$x_4\$ should be split into two states) OR you should be carrying the \$x_4\$  through to simplify \$\dot{x_4}\$ to a scalar in your analysis of the system. Usually states are scalars at least with my experience with nonlinear control.

$$\left(  \begin{bmatrix} u_2 \\ u_3 \end{bmatrix}+ \begin{bmatrix} \frac{-l K_4}{l_1} &amp; 0 \\ 0 &amp; \frac{-l K_4}{l_1} \end{bmatrix} \right) x_4 $$