# State Space model of a differential eqn. for use in Least Squares

The code in this page solves the Least Squares problem for the following dynamic model:

$\dot{y}=ay+bu$

where $a$ and $b$ are constants, $u$ is an input. The code is as follow:

t=[0:0.1:10];
m=length(t);
y=zeros(m,1);
a=-1;b=1;c=1;d=0;u=[100;zeros(m-1,1)]; % u: impulse with magnitude of 100

What's is not clear to me is why $a=-1$ and $b=1$. The model as given does not specify a value for either of $a$ and $b$. ($c=1$ and $d=0$ are fine, however).