piecewise chaotic map

here is my main piecewise funcation. I did the code just like the logstic map

function code()
  %Initialization Starts
  clc
  clear all
  close all               

    %lots of constants here
    %define rimax, Ri, P1, P2, n1 and n2
    f = 0:0.01:20; % f is in the P function
    r1 = 0.384;
    r1 = R(r1);

    for i=1:n
        r1 = R(r1);
    end
    for k = 1:N
        r1 = R(r1);
        y1(k,:) = r1;
    end
    y1=sort(y1);
    plot(f,y1,'k.','MarkerSize',1)
    xlabel('f')
    ylabel('r1');
    set(gca,'xlim',[0 20]);

    %here is the function
    function r = R(r1)
        define P : P = something something
        r = zeros(size(P));        
        % piecewise function here
        r(P<=0) = sqrt((Ri^2)*(1-P(P<=0)/P1).^-n1);
        r(P>0) = sqrt((rimax^2)-(rimax^2-Ri^2)*(1-P(P>0)/P2).^-n2);
    end
end

but the result is just a curve which I didn't expect

Anyone who could help me. I'm really confused.

Thank you!