MATLAB PID Filter Coefficient
<p>I have a problem in producing the algorithm of a PID with Filter Coefficient. The block diagram of the PID with Filter Coefficient looks like this.
<a href="https://i.stack.imgur.com/5pfIa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5pfIa.png" alt="enter image description here"></a></p>

<p>I found an algorithm/code in this link. <a href="https://www.mathworks.com/matlabcentral/answers/63762-filter-coefficient-n-in-pid-block" rel="nofollow noreferrer">https://www.mathworks.com/matlabcentral/answers/63762-filter-coefficient-n-in-pid-block</a></p>

<p><a href="https://i.stack.imgur.com/oWY9d.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oWY9d.png" alt="enter image description here"></a></p>

<p>Question: Why is that the FilterCoefficient has an unknown variable Filter_DSTATE which has an unknown variable of FilterCoefficient?
The code of FilterCoefficient has an unknown variable of Filter_DSTATE and the code of Filter_DSTATE has an unknown variable of FilterCoefficient?</p>

<p>Hypothesis. Is it one of them supposed to be initialize by some value?</p>