neighbhourhood preserving embeding algorithm

hello, I m working with neighbhourhood preserving embeding algorithm for ear recognition.

             XMX'a=LXX'a

         I need to solve the above equation to find 'a'.
         X-is the input image matrix.
         M-is a matrix.
         x'-is the transpose of the image matrix.
         L-is the eigon values 
    all the above values has been generated by the code in npe.m

can anyone please help me to solve the above equation to get 'a'.