function in for loop

I want to create an vector. The vector needs to get created in a forloop, using a function. so what i want it to become: R=(R1, R2, R3... RN)

But the problem is, after the loop the vector is like (0 0 0 0 ... RN) the part of my code that is important for this :

R=zeros(1,length(Numbers_used_P4))
for i=1:length(Numbers_used_P4)
CentreCircle(M,NumbersP4,x,y,d,i,P4_x,P4_y,xrel,yrel,R)
end

with the function

function [] = CentreCircle(M,NumbersP4,x,y,d,i,P4_x,P4_y,xrel,yrel,R)
  if M(i)<1
      Number=NumbersP4(i)
      x_4(i)=x(Number)
      y_4(i)=y(Number)
      dx(i)=xrel(Number)
      dy(i)=yrel(Number)
      d_4(i)=d(Number)
      Der(i)=dy(i)/dx(i)

        A(i)=1-M(i).^2
        B(i)=2*(M(i)^2)*d_4(i) ;
        C(i)=-M(i)^2*d_4(i)^2 ;

        D(i)=sqrt(B(i)^2-4*A(i)*C(i)) ;

        a_1(i)=(-B(i)+D(i))/(2*A(i)) ;
        a_2(i)=(-B(i)-D(i))/(2*A(i)) ;

        dc(i)=(a_1(i)+a_2(i))/2 ;

        ddx(i)=(dc(i)/d_4(i))*dx(i) ;
        ddy(i)=(dc(i)/d_4(i))*dy(i) ;

        ddx_A_1(i)=(a_1(i)/d_4(i))*dx(i);
        ddy_A_1(i)=(a_1(i)/d_4(i))*dy(i);

        ddx_A_2(i)=(a_2(i)/d_4(i))*dx(i);
        ddy_A_2(i)=(a_2(i)/d_4(i))*dy(i);

        A_1_x(i) = P4_x+ddx_A_1(i)
        A_1_y(i) = P4_y+ddy_A_1(i)

        A_2_x(i) = P4_x+ddx_A_2(i)
        A_2_y(i) = P4_y+ddy_A_2(i)

        C_x(i)=P4_x+ddx(i) ;
        C_y(i)=P4_y+ddy(i) ;

    else
        M_inv(i)=1/M(i)
        Number=NumbersP4(i)
        x_4(i)=x(Number)
        y_4(i)=y(Number)
        dx(i)=xrel(Number)
        dy(i)=yrel(Number)
        d_4(i)=d(Number)
        Der(i)=dy(i)/dx(i)

        A(i)=1-M_inv(i).^2
        B(i)=2*(M_inv(i)^2)*d_4(i) ;
        C(i)=-M_inv(i)^2*d_4(i)^2 ;

        D(i)=sqrt(B(i)^2-4*A(i)*C(i)) ;

        a_1(i)=(-B(i)+D(i))/(2*A(i)) ;
        a_2(i)=(-B(i)-D(i))/(2*A(i)) ;

        dc(i)=(a_1(i)+a_2(i))/2 ;

        ddx(i)=(dc(i)/d_4(i))*dx(i) ;
        ddy(i)=(dc(i)/d_4(i))*dy(i) ;

        ddx_A_1(i)=(a_1(i)/d_4(i))*dx(i);
        ddy_A_1(i)=(a_1(i)/d_4(i))*dy(i);

        ddx_A_2(i)=(a_2(i)/d_4(i))*dx(i);
        ddy_A_2(i)=(a_2(i)/d_4(i))*dy(i);

        A_1_x(i) = x_4(i)+ddx_A_1(i)
        A_1_y(i) = y_4(i)+ddy_A_1(i)

        A_2_x(i) = x_4(i)+ddx_A_2(i)
        A_2_y(i) = y_4(i)+ddy_A_2(i)

        C_x(i)= x_4(i)+ddx(i) ;
        C_y(i)= y_4(i)+ddy(i) ;
    end

    R(i)=abs(a_1(i)-dc(i))
    R2(i)=(abs(a_1(i))+abs(a_2(i)))/2

I've tried several things but I just don't get why it works like this

Answer 1

[Stephen23]

You need to output something from your function, most likely your want R and R1, e.g.

function [R,R1] = CentreCircle(M,NumbersP4,x,y,d,i,P4_x,P4_y,xrel,yrel,R)

and then in the loop you will need to allocate one or both of those outputs to some matrix, e.g.:

R = zeros(1,numel(Numbers_used_P4))
for k=1:numel(Numbers_used_P4)
    R(k) = CentreCircle(M,NumbersP4,x,y,d,k,P4_x,P4_y,xrel,yrel,R);
end

As you did not describe how your algorithm works, you will have to figure out the exact outputs that you need.

[Rens Jochemsen]

Thanx for your Answer Stephen, it was very helpful !

I already tried with the output, but only put in the function itself. I did not think of to put the output of the function into a vector R(i) in the script. It is the first time I use functions so I am not that good with them yet . Thanks for your help !

[Stephen23]

@Rens Jochemsen: the scoping rules means that MATLAB variables generally only appear in a workspace if you have explicitly put them there. Some exceptions exist (e.g. nested functions), but generally you should always pass values explicitly as input/output arguments (this is also the most efficient way to pass data between workspaces):

https://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

Answer 2

[Torsten]

R=zeros(1,length(Numbers_used_P4))
for i=1:length(Numbers_used_P4)
  R(i) = CentreCircle(M,NumbersP4,x,y,d,i,P4_x,P4_y,xrel,yrel)
end

function R = CentreCircle(M,NumbersP4,x,y,d,i,P4_x,P4_y,xrel,yrel)
...
R = ...;

Best wishes

Torsten.

[Rens Jochemsen]

Thanx for your anwer Torsten, it was very helpful!