How this PCA code written here .can someone plz explain.

Im adding this PCA function into DWTPCAv code but i dont undrstand what is happening with this code.here ca is the dwt coefficient plzz help

[ca{i},ch{i},cv{i},cd{i}] = dwt2(a{i},'db3');

[fca m1]=fuse_pcaany(ca,n);

function [y1 a1] = fuse_pcaany(ca,n)
for i=1:1:n
    M(:,i)=ca{i}(:);
end 
[V, D] = eig(cov(M));
[z1 s1] = size(D);
for i=1:1:s1
    D1(i)=D(i,i);
end 
D2=max(D1(i));
for i=1:1:s1
    if D1(i)==D2;
        a1 = V(:,i)./sum(V(:,i));
    end
end
[z2 s2]=size(ca{1});
% and fuse
y1=zeros(z2,s2);
for i=1:1:n
    y = a1(i)*ca{i};
    y1=y1+y;
end