Matlab Project 3: Questions and Answers

1. Question:
   In part b we are supposed to find the DTFT of the sinc function defined in part a. Where I am having trouble is that it asks for the DTFT over an interval of 2048 points. The sinc function is defined over a period of 125 points. Can you give me a hint on how to fix the indices so that the DTFT is over the right amount of points?
   
   Answer:
   The FFT command can be used to compute more samples of the FFT than you have points in the signal. In other words, if you have a signal x of length 125 (like your sinc function). You can say Xw=fft(x,2048) and that will give you 2048 samples of the DTFT between 0 and 2pi stored in the vector Xw.
   
   The command fft(x,N) computes N samples of the DTFT between 0 and pi provided that the signal x is of length less than or equal to N. See Section 5.1 of your Matlab book for more info on using the fft command to compute samples of the DTFT.


2. Question:
   I think that the sinc function in Matlab has a built in pi. Do we need to include the pi when we make a vector using sinc function?
   
   Answer:
   Matlab does build the pi into the sinc function, so you don't need to provide that as part of the argument. Type "help sinc" at the Matlab prompt for more information on the sinc function.


3. Question:
   Even after reading your hint about part g, my group and I are still confused on how to prove the property that they are asking us to prove. We were able to show it with Matlab. I looked in chapter 5 but I did not see anything that helped me. What section in chapter 5 will help us to do this proof?
   
   Answer:
   I'm glad to hear that the numerical "proof" worked out. I suggest you read Section 5.7 of the textbook for help in preparing your analytical proof.


4. Question:
   Is it okay to add pencil sketches and hand derivations within the report body?
   
   Answer:
   I have no objection to hand-drawn sketches and handwritten analytical derivations, as long as they are done neatly. I can see where it might be easier to write out the derivation than to try to type it into Word or other software.