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Changing the values of an array with an if condition inside a for-loop

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Eneko Cubillas Laiseca
Eneko Cubillas Laiseca on 2 Apr 2020
Hi everyone,
So I have this code:
% Repulsive forces (Fr)
rho_r = sqrt((x-xo).^2+(y-yo).^2);
if rho_r > rho_0
Fr(1,1) = 0;
Fr(2,1) = 0;
elseif rho_r <= rho_0
Fr(1,1) = Fr(1,1)-Kr*(x-xo)*((rho_r-rho_0)/rho_r);
Fr(2,1) = Fr(2,1)-Kr*(y-yo)*((rho_r-rho_0)/rho_r);
end
Frc = [Frc Fr];
And the first values for x and y are as follow. The values inside the array xo and yo are:
x = 15
y = 10
xo = [20 30 35 50 65]
yo = [13 25 35 38 45]
As you can see with those values for x and y, the elseif should be operating however I still have Fr == 0. I've tried some things out but it still doesn't work. I even created a for loop just as followed:
rho_r = sqrt((x-xo).^2+(y-yo).^2);
for i = 1:5
if rho_r(1,i) > rho_0(1,i)
Fr(1,i) = 0;
Fr(2,i) = 0;
elseif rho_r(1,i) <= rho_0(1,i)
Fr(1,i) = Fr(1,i)-Kr*(x-xo(1,i))*((rho_r(1,i)-rho_0(1,i))/rho_r(1,i));
Fr(2,i) = Fr(2,i)-Kr*(y-yo(1,i))*((rho_r(1,i)-rho_0(1,i))/rho_r(1,i));
end
end
Sorry my bad i forgot to add the values of rho_0 and Kr:
rho_0 = [7 4 5 3 4];
Kr = [500 350 500 250 250];
I've attached the full code

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Answers (1)

Birdman
Birdman on 2 Apr 2020
Edited: Birdman on 2 Apr 2020
Maybe the following code will get you going:
x = 10;
y = 10;
xo = [20 30 35 50 65];
yo = [13 25 35 38 45];
rho_r = sqrt((x-xo).^2+(y-yo).^2);
%dummy data
rho_0=30;
Kr=5;
%initial Fr
Fr=zeros(1,numel(xo));
%change values based on conditions
Fr(rho_r > rho_0)=0;
temp=-Kr*(x-xo)*((rho_r-rho_0)/rho_r);
Fr(rho_r <= rho_0)=temp(rho_r <= rho_0)
EDIT:
rho_r>rho_0
ans =
1x5 logical array
1 1 1 1 1
which means that every value in rho_r is greater than every corresponding value in rho_0. Therefore the following line
Fr(rho_r > rho_0)=0;
works and Fr becomes
Fr =
0 0 0 0 0

  2 Comments

Eneko Cubillas Laiseca
Eneko Cubillas Laiseca on 2 Apr 2020
Thanks a lot, the program is working better but I still have to make some adjustements in order for it to work to its absolut best.
Eneko Cubillas Laiseca
Eneko Cubillas Laiseca on 2 Apr 2020
I've added a condition to your code and it works better. Still have to do some more but thanks you very much :)!
rho_r = sqrt((x-xo).^2+(y-yo).^2);
for i = 1:2
Fr=zeros(i,numel(xo));
end
Fr(rho_r > rho_0)=0;
temp=-Kr.*(x-xo).*((rho_r-rho_0)/rho_r);
Fr(rho_r <= rho_0) = temp(rho_r <= rho_0);
Frc = [Frc Fr];

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