% PCA
m=mean(X,2);
M=400;
Z=X;
for i=1:M
Z(:,i)=(Z(:,i)-m);
end
[U,S,V]=svd(Z,0);
s1=0;
for i=1:400
s1=s1+S(i,i);
end
s2=0;
for i=1:400
s2=s2+S(i,i);
if s2/s1>0.90
break;
end
end
p=i;
imgreduction=X'*U(:,1:p);