How to change values from negative to positive and vicer versa in a loop

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Scott Banks
Scott Banks 2025-3-16
回答： Voss 2025-3-16
Dear Everyone;
I have created a for loop to compute certain values. Within the loop if Mw, Mx, My and Mz comes out of as a postive number I want to change it to a negative; and if Mw, Mx, My and Mz comes out of as a negative number I want to change it to a positive.
I have tried to do this with "If Statements", but the set of values come out as all positive or all negative.
Here is my code:
clear, clc, close all
% Distribution factor
DF = [0.4444 0.5556 0.5714 0.4286];
% Starting bending moments
M1 = (-25 + 20)*DF(1);
M2 = (-25 + 20)*DF(2);
M3 = (-20 + 4.67)*DF(3);
M4 = (-20 + 4.67)*DF(4);
for i = 1:8
% carry over
cf1 = M1/2;
cf2 = M2/2;
cf3 = M3/2;
% First distribution
Mw(i) = (0 + cf3)*DF(1)
Mx(i) = (0 + cf3)*DF(2)
My(i) = (0 + cf2)*DF(3)
Mz(i) = (0 + cf2)*DF(4)
% If Mw, Mx, My and Mz is positive change to a negative value
if Mw(i) > 0
Mw(i) = -(Mw(i))
% If Mw, Mx, My and Mz is negative change to a positive value
elseif Mw(i) < 0
Mw(i) = abs(Mw(i))
end
M1 = Mw(i);
M2 = Mx(i);
M3 = My(i);
M4 = Mz(i);
As you can see I have only attempted this with Mw. This is just to practise. Once I get the correct results I will include Mx, My and Mz.
Can someone help please?

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采纳的回答

Voss
Voss 2025-3-16
Ran in:
clear, clc, close all
% Distribution factor
DF = [0.4444 0.5556 0.5714 0.4286];
% Starting bending moments
M1 = (-25 + 20)*DF(1);
M2 = (-25 + 20)*DF(2);
M3 = (-20 + 4.67)*DF(3);
M4 = (-20 + 4.67)*DF(4);
for i = 1:8
% carry over
cf1 = M1/2;
cf2 = M2/2;
cf3 = M3/2;
% First distribution
Mw(i) = -(0 + cf3)*DF(1);
Mx(i) = -(0 + cf3)*DF(2);
My(i) = -(0 + cf2)*DF(3);
Mz(i) = -(0 + cf2)*DF(4);
M1 = Mw(i);
M2 = Mx(i);
M3 = My(i);
M4 = Mz(i);
end
Mw
Mw = 1×8
1.9464 -0.1764 0.1545 -0.0140 0.0123 -0.0011 0.0010 -0.0001
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
Mx
Mx = 1×8
2.4334 -0.2205 0.1931 -0.0175 0.0153 -0.0014 0.0012 -0.0001
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
My
My = 1×8
0.7937 -0.6952 0.0630 -0.0552 0.0050 -0.0044 0.0004 -0.0003
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
Mz
Mz = 1×8
0.5953 -0.5215 0.0472 -0.0414 0.0038 -0.0033 0.0003 -0.0003
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

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