How to convert all array values into negative ones?

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Lu Da Silva
Lu Da Silva 2022-1-31
编辑： John D'Errico 2022-1-31
I have an array A:
A = [2; 3; 5; -8; 9; 1; -1]
how do I convert it into an array whose values are all negative? So as to obtain B:
A = [-2; -3; -5; -8; -9; -1; -1]
Thanks!

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采纳的回答

KSSV
KSSV 2022-1-31
Ran in:
A = [2; 3; 5; -8; 9; 1; -1] ;
A(A>0) = -A(A>0)
A = 7×1
-2 -3 -5 -8 -9 -1 -1

更多回答（3 个）

Burhan Burak AKMAN
Burhan Burak AKMAN 2022-1-31
Ran in:
You can do like.
A = [2; 3; 5; -8; 9; 1; -1];
A = -(A.*A).^0.5;
A = 7×1
-2 -3 -5 -8 -9 -1 -1
Walter Roberson
Walter Roberson 2022-1-31
Ran in:
A = [2; 3; 5; -8; 9; 1; -1]
A = 7×1
2 3 5 -8 9 1 -1
%way #1
A(A>0) = -A(A>0)
A = 7×1
-2 -3 -5 -8 -9 -1 -1
%way #2
A = [2; 3; 5; -8; 9; 1; -1]
A = 7×1
2 3 5 -8 9 1 -1
A = -abs(A)
A = 7×1
-2 -3 -5 -8 -9 -1 -1
John D'Errico
John D'Errico 2022-1-31
编辑：John D'Errico 2022-1-31
Ran in:
So many ways. Don't forget the simple solution:
A = [2; 3; 5; -8; 9; 1; -1]
A = 7×1
2 3 5 -8 9 1 -1
B = -abs(A) % this makes all of the signs positive, then negates the entire lot
B = 7×1
-2 -3 -5 -8 -9 -1 -1
Or we could do this:
C = -sign(A).*A % this is similar to the use of abs
C = 7×1
-2 -3 -5 -8 -9 -1 -1
Those ways act on the entire array. In order to act only on those that have the wrong sign and do it effectively in place, the standard MATLAB solution would be this:
A(A > 0) = -A(A > 0)
A = 7×1
-2 -3 -5 -8 -9 -1 -1

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