The conditional statements of 2-PAM,8PAM and 16PAM

I take this: https://www.mathworks.com/matlabcentral/fileexchange/19587-symbol-error-rate-in-4-pam-modulation as a reference to write the code of 2-PAM,8PAM and 16PAM,but i am not sure why do we need to use the -2/sqrt(5) to be a boundary to decide which is -3 or 3 or -1 or 1 instead of using -1/sqrt(5) or -3/sqrt(5)

ipHat(find(r< -2/sqrt(5))) = -3;
ipHat(find(r>= 2/sqrt(5))) = 3;
ipHat(find(r>=-2/sqrt(5) & r<0)) = -1;
ipHat(find(r>=0 & r<2/sqrt(5))) = 1;

So,i want to ask someone to tell is my conditional statements of 2-PAM,8PAM and 16PAM right or wrong.

2PAM:

receiver_constellation( find(receiver< 0/sqrt(1) ) )= -1;
receiver_constellation( find(receiver>= 0/sqrt(1))  ) = 1;

8PAM:

receiver = real(complx_receiver); % taking only the real part
receiver_constellation(find(receiver< -6/sqrt(21))) = -7;
receiver_constellation(find(receiver>= -6/sqrt(21)  & receiver<-4/sqrt(21))) = -5;
receiver_constellation(find(receiver>= -4/sqrt(21)  & receiver<-2/sqrt(21))) = -3;
receiver_constellation(find(receiver>= -2/sqrt(21)  & receiver<0)) = -1;
receiver_constellation(find(receiver>= 0  & receiver<2/sqrt(21))) = 1;
receiver_constellation(find(receiver>= 2/sqrt(21) & receiver<4/sqrt(21))) = 3;
receiver_constellation(find(receiver>= 4/sqrt(21) & receiver<6/sqrt(21))) = 5;
receiver_constellation(find(receiver>= 6/sqrt(21))) = 7;

16PAM:

receiver = real(complx_receiver); % taking only the real part
receiver_constellation (find(receiver< -14/sqrt(10.5000))) = -15;
receiver_constellation( find(receiver>= -14/sqrt(10.5000)  & receiver<-12/sqrt(10.5000)) ) = -13;
receiver_constellation(find(receiver>= -12/sqrt(10.5000)  & receiver<-10/sqrt(10.5000))) = -11;
receiver_constellation(find(receiver>= -10/sqrt(10.5000)  & receiver<-8/sqrt(10.5000))) = -9;
receiver_constellation(find(receiver>= -8/sqrt(10.5000)  & receiver<-6/sqrt(10.5000))) = -7;
receiver_constellation(find(receiver>= -6/sqrt(10.5000)  & receiver<-4/sqrt(10.5000))) = -5;
receiver_constellation(find(receiver>= -4/sqrt(10.5000)  & receiver<-2/sqrt(10.5000))) = -3;
receiver_constellation(find(receiver>= -2/sqrt(10.5000)  &  receiver<0)) = -1;
receiver_constellation(find(receiver>= 0  & receiver< 2/sqrt(10.5000))) = 1;
receiver_constellation(find(receiver>= 2/sqrt(f10.5000) & receiver<4/sqrt(10.5000))) = 3;
receiver_constellation(find(receiver>= 4/sqrt(10.5000) & receiver<6/sqrt(10.5000))) = 5;
receiver_constellation(find(receiver>= 6/sqrt(10.5000) & receiver<8/sqrt(10.5000))) = 7;
receiver_constellation(find(receiver>= 8/sqrt(10.5000) & receiver<10/sqrt(10.5000))) = 9;
receiver_constellation(find(receiver>= 10/sqrt(10.5000) & receiver<12/sqrt(10.5000))) = 11;
receiver_constellation(find(receiver>= 12/sqrt(10.5000) & receiver<14/sqrt(10.5000))) = 13;
receiver_constellation(find(receiver>= 14/sqrt(10.5000))) = 15;

Hoping someone can tell me,thanks a lot