%PREX_EIGENFACES   PRTools example on the use of images and eigenfaceshelp prex_eigenfacesecho on              % Load one image per each subject (may take a while)  a = faces([1:40],1);              % Compute the eigenfaces  w = pca(a);              % Display them  newfig(1,3); show(w); drawnow;              % Project all faces onto the eigenface space  b = [];  for j = 1:40    a = faces(j,[1:10]);    b = [b;a*w];    % Don't echo loops    echo off  end  echo on              % Show a scatterplot of the first two eigenfaces  newfig(2,3)  scatterd(b)  title('Scatterplot of the first two eigenfaces')              % Compute leave-one-out error curve  featsizes = [1 2 3 5 7 10 15 20 30 39];  e = zeros(1,length(featsizes));  for j = 1:length(featsizes)    k = featsizes(j);     e(j) = testk(b(:,1:k),1);     echo off  end  echo on              % Plot error curve  newfig(3,3)  plot(featsizes,e)  xlabel('Number of eigenfaces')  ylabel('Error')echo off