Matlab: optimize code

Problem: I have the trajectories of 14 users: I have compare the trajectories of every user and for each one, I have calculated the longest common sequence: TrajSimilarity(1,k).aLongestString. Now I want to compare the longest common sequence of the first user with the others, the longest common sequence of the second user with the others and etc.   I have no problems to compare the longest common sequence of two users using this code:   string3=TrajSimilarity(1,3).aLongestString; string4=TrajSimilarity(1,4).aLongestString; [D,dist,aLongestString]=LCS(string3,string4); U=numel(regexp(string3,'(\(\d+\)|\d)')); V=numel(regexp(string4,'(\(\d+\)|\d)')); nLCS=numel(regexp(aLongestString,'(\(\d+\)|\d)')); ratioU=nLCS/U; ratioV=nLCS/V; EA = (ratioU + ratioV)/2; WA = (U*ratioU+V*ratioV)/(U+V); LCS is a function that calculates the longest common substring between two strings (if can be helpful, I will post a link with it). I have problems to create an optimized code that compare the longest common sequence of the first user with the others, the longest common sequence of the second user with the others and etc. I try this code:   for k=1:14 string3=TrajSimilarity(1,k).aLongestString; for j=2:14 string4=TrajSimilarity(1,j).aLongestString; [A(k,j).D,A(k,j).dist,A(k,j).aLongestString]=LCS(string3,string4); end end but it generates error:   Attempted to access L(0,0); index must be a positive integer or logical. Error in LCS (line 52) dist = L(n,m); Error in Prova1 (line 6) [A(1,k).D,A(1,k).dist,A(1,k).aLongestString]=LCS(string3,string4); Can you give me an help?