You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: BL_EVD.m
    path of file: ./repos/lrslibrary/libs/SVD
    
    the code of the file until where you have to start completion: 
function [U1,S]=BL_EVD(A,U0,k)

% Jan 2010
% This matlab code implements the block lanczos method with k steps
% for partial EVD.
%
% A - m * m symmetric matrix (required input)
% U0 - Initial subspace (required input)
% k - the number of blocks
%
% U1 - Output subspace, eigenvectors
% S - eigenvalues
%
%
% Reference: Zhouchen Lin and Siming Wei, A Block Lanczos with Warm Start 
% Technique for Accelerating Nuclear Norm Minimization Algorithms, 
% arxiv: 1012.0365.
%
% Bug report: zclin2000@hotmail.com
%


    
function [U1,S]=BL_EVD(A,U0,k)

% Jan 2010
% This matlab code implements the block lanczos method with k steps
% for partial EVD.
%
% A - m * m symmetric matrix (required input)
% U0 - Initial subspace (required input)
% k - the number of blocks
%
% U1 - Output subspace, eigenvectors
% S - eigenvalues
%
%
% Reference: Zhouchen Lin and Siming Wei, A Block Lanczos with Warm Start 
% Technique for Accelerating Nuclear Norm Minimization Algorithms, 
% arxiv: 1012.0365.
%
% Bug report: zclin2000@hotmail.com
%


if nargin < 2
    error('Too few arguments') ;
elseif size(A,1)~=size(A, 2) || norm(A-A','fro')>1e-8*norm(A,'fro')
    error('A should be symmetric!');
end