how to calculate SNR in Mr x Mt MIMO channel matrix?

I got the code below through github. (about MIMO antenna selection code)

But I have one question.

I was wondering how you got the SNR from the channel matrix composed of Mr x Mt.

And what does 0.707 multiplied by the channel matrix mean?

% Antenna parameters
Mr = 16;
Mt = 16;
fullAntennas = (1: Mr);

% Mr x Mt-based channel matrix H
H = randn(Mr,Mt) +1j*randn(Mr,Mt);
H = 0.707*H;

% temp buffer
SNRs = [];

% what is this?
% How did you calculate SNRs?
% What formula did you use in the code to get the SNRs for the channel matrix?
for i=1:length(fullAntennas)
    SNRs = [SNRs; sum(H(i,:).^2)];
end