How to create a chirp function in Matlab?

In Matlab, I am amtempting to write a function that creates a chrip signal. I do not want to use the chirp function itself. I feel like I am missing something. My code is not working properly and I am not sure why. It does not alias correctly when it should and the sound does not change adjusting the frequency.

function [xx,tt]=mychirp(f1,f2,dur,fs) 
%f1= starting frequency
%f2=end frequency
%fs=sampling frequency
tt=0:1/fs:dur; %Creates sampling window
m=(f2-f1)/(2*dur); %Calculating alpha/slope
s=2*pi*cos(m*tt.^2 +f1*tt);
soundsc(s,fs)
spectrogram(s,1024,[],1024,fs,'yaxis')

What am i missing here?

Answer 1

[Star Strider]

This creates ‘sort of’ chirp function:

[f1, f2, dur, fs] = deal(0, 1000, 2000, 8192);
tt=0:1/fs:dur; %Creates sampling window
m=(f2-f1)/(2*dur); %Calculating alpha/slope
s=2*pi*cos(m*tt.^2 +f1*tt);
soundsc(s,fs)
spectrogram(s,1024,[],1024,fs,'yaxis')

What do you want to create?