MSE and PSNR code for image

I'm calculating MSE and PSNR values for an image. Following is the code for it. Can you explain this code ? It seems quite complicated. I think m, n, d are height, width, length respectively.

a=imread('colorlable.jpg');

[m,n,d]=size(a);

kmax=floor((m*n)/(m+n+1));

da=double(a);

U=zeros(m,m);S=zeros(m,n);V=zeros(n,n);e=zeros(kmax,d);cr=zeros(kmax,1);rmse=zeros(kmax,d);

for i=1:d

[U(:,:,i),S(:,:,i),V(:,:,i)]=svd(da(:,:,i));

end

for k=1:kmax

ca=zeros(m,n,d);

MSE=m*n/(k*(m+n+1));

fprintf('MSE value at %f.\n',MSE);

SNR =(10*log10((sum(m.^2)))/MSE);

fprintf('PSNR value at %4f.\n',SNR);

end