Talk:ECE 280/Spring 2010

When posting questions, please be sure to use the Q Template so the instructor and TAs will see the question. Note in the examples below the Q Template has been removed to indicate that the question has been answered.

Questions about particular lectures

Lecture 2 - 1/15

• Here is a sample question - how does Euler's Relationship work for complex exponentials? DukeEgr93 17:55, 15 January 2010 (EST)
  • There are a few different ways to show Euler's relationship, one of which involves Taylor/Maclaurin Series Approximations for cos, sin, and e. See Euler Notation on the (as yet not complete - but finished enough for this example) Complex Numbers page for more detailed information. DukeEgr93 17:55, 15 January 2010 (EST)

Questions about particular homework assignments

Homework 1

• Here is a sample question - how do I get access to the code from class that seems really relevant to this assignment? DukeEgr93 17:55, 15 January 2010 (EST)
  • All codes written in class will go in my ~mrg/ECE54 folder with each day having its own folder. If you use code developed in class. be sure that the comments section at the top of the code indicates that the code is a modified form of my code. Something on the order of:

% [Function or Script Name]
% [Your Name]
% [Date Written]
% Based in part on:
% [Original Function or Script Name]
% [Original author name]
% Accessed on: [Date accessed]

% With my NET ID as a signature, I hereby indicate that I understand and
% have followed the Duke Community Standard in completing this assignment
% Signed: [Your NET ID]

should work. DukeEgr93 17:55, 15 January 2010 (EST)

• When deciding whether a signal is periodic or not, does the phase shift factor in at all? Mdo9 20:06, 16 January 2010 (EST)
  • The phase not not change the periodicity of a signal at all; the phase generally only serves to indicate when a maximum, minimum, or other value happens. DukeEgr93 02:02, 17 January 2010 (EST)

• On a similar note, does this phase shift affect what exactly the fundamental period would be given two combined signals with different phases? Or is this still irrelevant? Mdo9 02:46, 17 January 2010 (EST)
  • Almost irrelevant to whether or not the combined signal is periodic and what the period is - with one set of exceptions: complete deconstructive interference. For example, if you are putting together three signals and two of them just happen to cancel each other out, then the period of the overall signal would be the same as the signal that remains. That is to say, if you are looking at \(\begin{align} x_1(t)&=\cos(t) & x_2(t)&=\sin(\pi t) & x_3(t)&=\cos(t+\phi) \end{align}\) and trying to determine if \(\begin{align} y(t)&=x_1(t)+x_2(t)+x_3(t) \end{align}\) is periodic, then for most values of \(\phi\) the signal \(y(t)\) will not be periodic since the component periods do not form rational fractions. However, if \(\phi\) happens to be \(\pi\) rad (or some angular equivalent to it), then \(x_1(t)\) and \(x_3(t)\) would cancel out, leaving just \(x_2(t)\) and in that specific instance, \(y(t)\) would be a periodic signal with period \(T=2\) sec.

    Otherwise, however, the phase does not have an impact on whether a combined signal is period and, if it is, on what the period of a combined signal would be. DukeEgr93 09:24, 17 January 2010 (EST)

• Part I of HW1 states that we must determine whether a function is periodic or not. Does this mean that we must provide a proof for each function, or can we just state a(t) is periodic with period xx and b(t) is not periodic? Tbg4 16:03, 17 January 2010 (EST)tbg4
  • You do not have to show proof the periodicity, per se, but you should show work in determining what the period is if it is periodic. My fault for not putting enough direction in the problem statement... DukeEgr93 18:55, 17 January 2010 (EST)

• When constructing a MATLAB plot for a piecewise function with jump discontinuities (such as a square wave), I am having trouble getting these to 'show up' correctly in the final plot - the jumps are connected more by large-sloped lines than straight vertical ones; I realize this is probably just a limitation of the way the math/MATLAB is dealing with this, but is this type of graphical imperfection 'ok' to turn in for this assignment? Mdo9 16:43, 18 January 2010 (EST)

General questions

• I can't find a working link for xwin. Tbg4 18:07, 17 January 2010 (EST)tbg4
  • X-Win? Which links were broken? DukeEgr93 18:55, 17 January 2010 (EST)