MATLAB Function is used to display the graph of the twice derivative using Matlab's simulink.

ddx $=-$dx $-3*($x$+$y$)-($dx$*$dy$)^2+2$

ddy $=-6*$dy $+3*($x$+$y$)+5*$sin$(3*$t$)-$k$*$y

If dy $>=0,$make a circuit that represents k $=-1,$and

if dy k $=1.$

$($I made it like the picture above, but please let me know what's wrong and what I should do$.)$