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

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

Answer 1

[Birdman]

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

[Eneko Cubillas Laiseca]

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]

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];