How can I track the total number of node infections from a set of random seed nodes each? I tried using the v = bfsearch(G,s) command but I got an error report: Error using search (line 27) Starting node must specify one node.

clear all
load('nodenetwork.mat');        
network = A;
N=size(network,1);                                                        
beta=0.12;
gama=0.3;
deadline=20;                                                               
flag=zeros(1,N);                                                          
bnet=graph(network);

k=randperm(N);                                                            
randnodes=randsample(k,4);                                                         

flag(randnodes)=1;                                                        

for i=1:N
            if flag(i)==1                                                  
                %infect its neighbor
                neighbor=find(network(i,:)==1);                          
                for j=1:length(neighbor)                                   
                    pinf=rand();
                    if (pinf>=beta)&&(flag(neighbor(j))==0)              
                        flag(neighbor(j))=1;
                    end
                    speff=bfsearch(bnet, randnodes);
                end
                %rocovered
                precv=rand();
                if (precv>=gama) && (pinf < beta)                         
                    flag(i)=2;
                    network(i,:)=0;
                    network(:,i)=0;
                end
            end
end

%the number of S
S=length(find(flag==0));
%the number of I
I=length(find(flag==1));
%the number of R
R=length(find(flag==2));