Vector with various IFs, adding up and counting down

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dirk-jAn
dirk-jAn 2018-6-19
评论： dirk-jAn 2018-8-18
I need to translate an Excel formula to whatsapp.
I have one vector X: [ 5 2 -4 -6 -2 1 4 2 -3 -6 -1 8 9 ]
Now, vector y needs to accumulate if vector x is negative and the opposite when positive until back to zero: [ 0 0 -4 -10 -12 -11 -7 -5 -8 -14 -15 -7 0 ]
I have been looking through Matlab functions but don't come far. Is there any easy way to do this on Matlab?
Many thanks in advance!

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回答（1 个）

Paolo
Paolo 2018-6-19
X = [ 5 2 -4 -6 -2 1 4 2 -3 -6 -1 8 9 ];
indx = find(X<0);
Y = [zeros(1,indx(1)-1) cumsum(X(indx(1):end))];
Y(Y>0) = 0;
Y =
Columns 1 through 11
0 0 -4 -10 -12 -11 -7 -5 -8 -14 -15
Columns 12 through 13
-7 0
  2 个评论
dirk-jAn
dirk-jAn 2018-8-16
Thanks Paolo. This answer indeed solves perfectly the example I gave. However, if the series are longer and come back into negative after some positive values, the positive values should not be added up, so a negative value should directly lead to a decrease below 0, e.g.:
X: [ 5 2 -4 -6 -2 1 4 2 -3 -6 -1 8 9 5 -6 -11]
should not be
[ 0 0 -4 -10 -12 -11 -7 -5 -8 -14 -15 -7 0 0 0 -10 ] as it is now, but should be:
[ 0 0 -4 -10 -12 -11 -7 -5 -8 -14 -15 -7 0 0 -6 -17]
In other words, positive numbers between series of negatives should be treated the same as the positive numbers at the very start.
Again thanks in advance for solving this.
dirk-jAn
dirk-jAn 2018-8-18
I think it is solved:
X = [ 5 2 -4 -6 -2 1 4 2 -3 -6 -1 8 9 5 -6 -11];
X(X(1)>0)=0;
Y=X;
for n=2:length(X)
if sum(Y(n-1:n)) > 0
Y(n)=0;
else
Y(n)=sum(Y(n-1:n));
end
end

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