Interpolating the data given between -pi and pi

I have the following program and wanted to get the value between -π and π. But the program I made below only gives . Any help is apperciated

ts=1/21;
t=0:ts:1;
for k=1:lengtht(t)
    th(k)=(k-1)*2*pi/(length(t)-1)
end
Thanks 

Answer 1

[KSSV]

You can simply use

m = 100 ;   % get this value using your ts step size 
th = linspace(-pi,pi,m) ; 

Using the time step ts..simply use

ts = 1/21 ; 
th = -pi:ts:pi ;