invder.m

一个利用Matlab实现PCA（主成分分析）

function data_der=invder(data)
% data_der=invder(data)
% inverse 2nd derivative for making data2 matrix for simplisma

% written by K.Artyushkova
%7/7/1999

[n,m]=size(data);
for i=1:m
    Dmf = fourdifft(data(:,i),2);
    data2=sgolayfilt(Dmf, 3, 15);
    data_der(:,i)=data2*(-1);
end

for i=1:n
   for j=1:m
        if data_der(i,j)<=0,
         data_der(i,j)=0;
      end
   end
end