# How to convert all array values into negative ones?

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Lu Da Silva on 31 Jan 2022
Edited: John D'Errico on 31 Jan 2022
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!

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

Burhan Burak AKMAN on 31 Jan 2022
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
Sambit Supriya Dash on 31 Jan 2022
A(A>0) = -A(A>0)

Walter Roberson on 31 Jan 2022
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 on 31 Jan 2022
Edited: John D'Errico on 31 Jan 2022
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