error message Subscripted assignment dimension mismatch is showing.....

for j=1:l+1
       instt(1,:)=pir(1,:);
       instt(j)=13;
       for w=(j+1):(l+1)
           instt(w)=pir(w-1);
       end
   instt;
   end

i want to insert 13 to all possible position in the array pir (instt is the array used to store the result and to print it).

the error message is :Subscripted assignment dimension mismatch. it will be a great help if got to know why this happen,please help me......

[jithin jayasingh]

l is the length of array pir