pod orthogonal decomposition -　This function calculates the POD basis vectors



　Function inputs:

　X　　　 :　(n x nsnap) snapshot matrix

　　　　　　 n = number of states in full space

　　　　　　 nsnap = number of snapshots

　cenergy :　how much energy of the ensemble you want

　　　　　　 to capture, i.e. cenergy = 99.9 (percent)

　

　Function outputs:

　phi　　 :　 (n x nsnap) matrix containing POD basis vectors

　lam　　 :　 (nsnap x 1) vector containing POD eigenvalues

　Xmean　 :　 (n x 1) the mean of the ensemble X

　nbasis　:　 number of POD basis vectors you should use

　　　　　　　to capture cenergy (percent) of the ensemble