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how to add column of a matrix

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Monika Kok
Monika Kok 2016-4-25
评论： Walter Roberson 2016-4-27
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

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回答（1 个）

Roger Stafford
Roger Stafford 2016-4-25
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.)
  2 个评论
Monika Kok
Monika Kok 2016-4-27
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
Walter Roberson 2016-4-27
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

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