function [newpop]=mutation(oldpop,stringlength,a,b,pm)
pz=size(oldpop,1);
for i=1:pz
   if(rand<pm)
     mpoint=round(rand*(stringlength-1))+1;
     newpop=oldpop;
     newpop(i,mpoint)=abs(oldpop(i,mpoint)-1);
     sum=0;
     for j=1:stringlength
        sum=sum+newpop(j)*2^(j-1);
     end
    newpop(i,stringlength+1)=sum;%解碼   
    x(i)=newpop(i,stringlength+1);
    newpop(i,stringlength+2)=fitness(x,pz,stringlength);
  else 
     newpop=oldpop;
    
  end
end