Adding each row to previous row in a vector-Not Cumulative
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Hi , I've looked everywhere to find the solution for this but I couldn't find the answer. Here 's the problem. How to add each row in a vector with just the previous row? For example here is the process on this vector: A=[2 1 7 9 4] and the answer should be this vector: C=[3 8 16 13]
Thanks in advance.
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Accepted Answer
Sukuchha
on 20 Jul 2011
A=[2 1 7 9 4]; B = A(1:end-1)+diff(cumsum(A));
1 Comment
Jan
on 20 Jul 2011
diff(cumsum(A)) ?! An expensive method to get: A(2:end). But in addition there is the danger of rounding errors, e.g. diff(cumsum([1e16, 1, 5])) is [0, 4] ! Therefore I strongly recommend not to use this.
More Answers (3)
Jan
on 20 Jul 2011
Easier and faster:
B = A(1:end-1) + A(2:end)
2 Comments
Sukuchha
on 21 Jul 2011
Jan, your method is better ! i feel like stupid now ! I need to remember always solve problems in a simplier way !
Jan
on 21 Jul 2011
@Sukuchha: Often a direct translation of the human language is helpful. You've formulated your algorithm very clear already: "add each row in a vector with just the previous row". So you did solve the biggest part of the problem already. Most of the questions in this forum are much less clear.
Paulo Silva
on 20 Jul 2011
C=arrayfun(@(x)plus(A(x),A(x-1)),2:numel(A))
or with a for loop
C=zeros(1,size(A,2)-1);
for x=2:size(A,2)
C(x-1)=A(x)+A(x-1);
end
C
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