# CDS 101/110a - FAQ

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This page contains frequently asked questions for CDS 101/110a from 2006 on. Older FAQs for the course are available from another server:

- CDS 101/110, Fall 2003
- CDS 101/110, Fall 2004
- (No FAQs available for 2005)

## Week 1

- Can you make the graphics bigger so that we can see them?
- Can you speak more slowly?
- How are stability, performance, and robustness different? They seem very similar
- How do I create a FAQ for CDS 101/110?
- How would you make the dynamics in the cruise control example more realistic?
- I did not understand robustness
- I didn't catch the fly video. Is it available online?
- Is a high gain good in the speed control example?
- Is control a type of negative feedback?
- Is it possible to take CDS 110b without taking CDS 110a?
- Is it true that feedback systems are in closed loop by definition?
- Is kp (the gain of the system) dimensionless?
- Is there room for learning in control systems theory?
- Latency wasn't mentioned in the example; does it affect robustness?
- Please turn the AC higher.
- Should we bring our computers with Matlab installed to the review Friday?
- The additional material and schedule of cds210.
- The last few slides went by too fast
- What do you mean by "gain" in the speed control example? What relation to sensing does it have?
- What is an example of an open loop system
- What is the schedule for 101 in the 4th, 6th, & 8th weeks?
- What should we do with unsused Mud Cards?
- Where can I get a more detailed description of how the flyball governor works?
- Why does instability imply poor performance?

- Are there any advances in applying feedback modeling to social systems other than in an economic sense?
- Can I turn my homework by email (pdf file)?
- Can the environment be considered a system state?
- How do I save the mp3 files?
- How does feedback help the X-29 experimental aircraft?
- In lecture 1.2, y(x) was used as a function of the state variables. Is y a generic function of vector x?
- It's a bit unclear to me when you talk about "error" in PID control
- What are methods for determining errors in a real system?
- What is fuzzy logic?

- In problem 1 (CDS 110)/problem 2 (CDS 101), download cruise-ctrl.mdl, NOT cruisedyn.m
- Problem 1 -- Do I need to know exactly how a device works to use it as an example?
- Problem 2b -- Does this mean exactly or at least fifty percent?
- Problem 4 -- Do I have to sum n i(t)?
- SIMULINK License
- What is the policy for using symbolic manipulation on homework sets?

## Week 2

- Can a Lyapunov function be used to show/prove a system is unstable at an equilibrium point similar to the way it can be used to show asymp stability?
- How do we read the simulated predator-prey graph?
- How is the Internet a feedback system?
- I'm a 101/110 student. Can I sit in on the 210 lectures on Fridays without being enrolled in 210?
- In slide 12, what is special about the red cycle as opposed to the blue curves?
- In slide 9, why did you only linearize around the downward equilibrium point?
- Is q1 a function of time
- Is there any open source software we can use instead of MATLAB?
- What are the Di parameters in the power grid model?
- What does the 45 mean in ode45?
- What does the at symbol mean in front of a function in matlab?
- What is a finite state machine and how does it relate to the traffic example?
- What is the significance of having eigenvalues that are 0? I think I heard you say "in that case you don't know anything". Does that mean you cannot determine if the system is stable or asymptotically stable?
- What's the difference between control "over" network and control "of" network?
- Where can I find a theoretical definition of dynamical system?
- Why is dB defined as 20log 10?
- Why was there only one damper in the mass/spring model?
- You mentioned "aggressive" dynamics a couple of times. Please define. How/when is it useful?
- You said spiraling out to a bounded circle is unstable, but doesn't that still satisfy the epsilon-delta condition of stability? Or are there limits on epsilon?

- CDS210 Problem 4 typo
- Do we have to consider complex states when trying to find equilibrium points analytically?
- In problem 3 (CDS 110), please use a different V2(x).
- Phaseplot
- Problem 1 -- Can I use Maple or Mathematica to solve this?
- Problem 1 -- Why don't the units work?
- Problem 2 - Actuator block
- Problem 2 -- Saturation of signal u
- Problem 2b -- Do I need to include the controller and feedback?
- Problem 3 -- Does "output get smaller as k gets larger" mean it gets more negative or more closer to zero?
- There are some problems with Ex 6
- Why are the initial conditions of the integrator and engine in hw1cruise.mdl set to 55*50?

## Week 3

- Are the dynamics on slide 10 correct?
- Has a stable system a stable eq. point? a limit cycle?
- How are the z variables defined on slide 10, Lecture 3-1?
- How do equations given for dynamics on slide 10 relate to the state-space setup we used before?
- How do we choose epsilon in the definition of stability?
- How was V(x) derived on slide 13 of Lecture 3-1?
- Is the overshoot definition on slide 12 correct?
- Is the system on slide 5 stable?
- What is "closed form"?
- What is a plant in the context of this class?
- What is a stable system?
- Who/What is Lyapunov?

- Could you please make it clear what is an 'A' and what is a 'Lambda' (matrix)?
- Do complex matrices also have a Jordan canonical form?
- How do you actually find the Jordan canonical form of a matrix?
- I keep getting mixed up on whether the diagonalized form of A is T^(-1)AT or TAT^(-1). Is there an easy way to remember the correct form?
- Was the equation for V(q) for the spring mass example missing a transpose?
- What does "up to permutations" mean?
- Where can I find the proof to the Lyapunov Theorem?

## Week 4

## Week 5

- Can you recommend a good linear algebra resource?
- Could we move office hours?
- Do we always need to know everything about the states? The Segway example sort of suggests not.
- Does lim (t to infty) E(x-x hat) = 0 imply that there will be less disturbance over time?
- Is T completely arbitrary in the definition of reachability?
- What is matrix rank and how do i calculate it?

## Week 6

- Can you explain the axes of the Bode plot better?
- Does pole zero cancellation happen and is it useful?
- Intermediate steps in block diagram algebra for the Engine Control of a GM Astro example?
- What is G and what is H? What is the difference in the way they are defined?
- What is meant/useful about transfer functions between 2 blocks in a block diagram?

## Week 7

- "HW6 Question 3"
- Hw 6 Problem 2
- HW 6 Question 4
- If there is a common pole and zero (say at a) in the closed loop transfer function, should I say there's one pole at a and also one zero at a?
- In Problem 2b what does Mp mean?
- Matlab tips for using less paper.
- Problem 4a -- Change gain crossover to bandwith

## Week 8

- A typo in equation (6.24).
- How do I evaluate a certain transfer function at desired frequencies numerically?
- HW 7 Prob 1 Comments
- HW 7 Problem 2
- In MATLAB, use feedback() command to obtain the closed loop transfer function. Do not use L/(1 L).
- Problem 1 b and c -- Plot step and freq response
- Problem 1c - Ziegler-Nichols
- Problem 3d - Pay special attention to low Ti values
- Problem 4c -- Settling time
- When evaluating the Bode integral, I am not getting even close to the ideal result (something negative)?

## Week 9

- How is the slope of the gain curve related to robustness?
- HW8 Problem 1 Hints
- HW8 Problem 3
- HW8 problem 4
- Problem 1 -- What is the value of a?
- Problem 2 (CDS101) Problem 1 (CDS110)
- Problem 2 -- What does "less negative" mean?
- Problems 3c and 4b - Plot Nyquist plots cooresponding to the loop transfer function