function K = center(Ktst,Ktrn)%CENTER Center the kernel matrix%%   K = CENTER(KTST,KTRN)%% Center the kernel matrix KTST in the kernelspace defined by KTRN.%%@article{Scholkopf1998,%	author = {Bernhard Scholkopf and Alex J. Smola and Klaus-Robert%    M{\" u}ller},%	title = {Nonlinear Component Analysis as a Kernel Eigenvalue Problem},%	journal = {Neural Computation},%	year = {1998},%	volume = {10},%	number = {5},%	pages = {1299-1319}%}% Copyright: D.M.J. Tax, D.M.J.Tax@prtools.org% Faculty EWI, Delft University of Technology% P.O. Box 5031, 2600 GA Delft, The Netherlandsn = size(Ktrn,1);I = repmat(1/n,n,n);m = size(Ktst,1);I1 = repmat(1/n,m,n);K = Ktst - I1*Ktrn - Ktst*I + I1*Ktrn*I;return