PCA more efficient

S=xsn;
Hi, I have this code to calcule the first components from the PCA.
Anyone, can help me to writte down it more efficently.

Specifically to obtain the vector Ex:
I have consider the sum of components (ax) reach the 65% of the total contribution of the components,
but there are other form more efficiently to write dow it?.

FT=cov(S);
[evecs,evals]=eig(FT);
[sev,I]=sort(diag(evals))
nsa=length(sev);

ax=0;
Ex=[];
for i=nsa:-1:1

ax= ax+sev(i)/sum(sev);
Ex=[Ex evecs(:,i)];

if ax>0.85 % The sum of components have to account for 65% of the data variation.
break % We do not have account the rest of components.
end
end


cheers,
Jose.
.

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