Rearrange variable in same column and define new variable

I have a table of probabilities arranged in descending order.

Symbol---- Probability

S1 ---- 0.7188

S2 --- 0.0625

S3 --- 0.0625

S4 ---0.0469

S5---0.0313

S6---0.0156

S7---0.0156

S8---0.0156

S9--- 0.0156

S10--- 0.0156

Then, I need to add the two minimum probability and named as a1( for this case S9+S10 =a1=0.0312). The next table would be arranged in descending order.

Symbol---- Probability

S1 ---- 0.7188

S2 --- 0.0625

S3 --- 0.0625

S4 ---0.0469

S5---0.0313

a1 --- 0.0312

S6---0.0156

S7---0.0156

S8---0.0156

My question is, how can I arrange the second table with the corresponding symbols and delete the two smallest probabilities?

and lastly creating the next table until only two symbols are left. p/s the next sum of smallest probability is a2, a3 ... p/s mine is just for 2nd column

mat = [ 0.7188 0.0625 0.0625 0.0469 0.0313 0.0156 0.0156 0.0156 0.0156 0.0156 ];

%Assign symbol number to perspective probability 
for i = 1: length(mat)
      S(i) = mat (i);
      i= i+1;
end

%Adding the minimum probability
 a(1)=  S(end)+S(length(mat)-1);

 %Rearrange the probability 
   for i = 1:(length(mat)-2)
       mat2(i) = mat(i)
  % mat3 =sort([mat2(i) a(1)])
  i=i+1;
  end 
   mat3= sort([mat2 a(1)]);
   mat4 = sort(mat3,'descend');
   col2 = mat4';