how to add column of a matrix

a= [1 2 3 4 ; 1 0 1 6; 4 5 6 7; 1 0 3 3]

a(:,1) = a(:,1)+a(:,2);

i am using the above code but i would like to generate a for loop which will give me addition of column such as:

1)column 1 + column 2

2)[column1+column3] and [column1+column2+column3]

3)[column1+column4] and [column1+column2+column4] and [column1+column3+column4] and [column1+column2+column3+column4]

so taking first and last column and getting all the possible combination between them

thanks monica

Answer 1

[Roger Stafford]

   b = zeros(4,16);
   for k = 0:15
     t = double(dec2bin(k,4)-'0');
     b(:,k+1) = sum(bsxfun(@times,a,t),2);
   end

The sixteen columns of b give sums of all possible subsets of columns of a (including the empty set.)

[Monika Kok]

the thing which i want is lets say if i am using using column 1 and column 3 then they should be in every combination. only the column between them should provide a combination

[Walter Roberson]

   FirstCol = 1; LastCol = 4;

   colspan = LastCol - FirstCol - 1;
   num_arrange = 2^colspan;
   num_row = size(a,1);
   num_col = size(a,2);

   b = zeros(num_row, num_arrange);
   for k = 0 : num_arrange - 1
     t = [zeros(1, FirstCol-1), 1, fliplr(double(dec2bin(k,colspan)-'0')), 1, zeros(1, num_col - LastCol)];
     b(:,k+1) = sum(bsxfun(@times,a,t),2);
   end