writing a code for DFT without using built-in functions

Hello, I need to write a discrete fourier transform code without using any built-in functions.The code I am trying to get to work is:

f=1/2; //frequency

N=13; // total samples

n=0:1:N-1; //summation going from n=0 to n=12

x=cos(2*pi*f*n)*exp((-j*2*pi*n*k)/N); //I usually put k=1.

Xz= [(X) zeros(1,10)]; // padding with zeros

plot(abs(Xz)); //plotting the magnitude

the range is from 0 to 2*pi but I don't know how to code that as well? This is my first time using matlab so any help would be great.

The error I get is error using * Inner matrix dimensions must agree.

Answer 1

[dpb]

doc times

Since you say this is your first experience w/ Matlab, I suggest starting at the beginning of the online doc's are read at least the sections through the "Language Fundamentals" topic

[steven]

Thank you for the help. I have been reading through all the topics just trying to understand how matlab works.

Another question I have is how do I set the range from 0 to 2pi on the x-axis? when I use

y= linspace(0,2*pi);

plot((abs(Xz),y);

I get the error vectors must be the same length. Thanks again for any help.

[dpb]

Why do you name 0:2*pi as 'y' instead of x? Not that it really changes anything, but still, it's conventional, surely.

doc plot

Input syntax is given as

plot(X,Y,'linespec')

If you want the x-axis to be 0:2pi then plot the response versus that vector instead of vice-versa. And, of course, the length(Y) and length(X) must be the same.