Secant Method not Working, Please Help!

my code isnt working , i need help fixing my secant method so that it updates every guess with every iteration. i need the guess 1 to update to guess 2 from the last iteration and i need guess 2 to update to the root found from the secant method. i need to find a root for each of the f in a range of 1 to 750. Any help is appreciated, this project is due tommorow.

%% parameters
% Aluminum plate E = 69GPa, v = 0.3269, p = 2700 kg/m^3
% Copper E = 117 GPa, v = 0.34, p= 8920 g/cm^3
E = 69e9;
p =  2700;
v = .3269;

c1 = sqrt((E*(1-v)) / (p*(1+v)*(1-2*v)));      % Pwave (m/s)
c2 = sqrt(E / (2*p*(1+v)));       % S wave (m/s)

f = 1e3:1e3:750e3; % 1 to 750 khz (we can choose step size)(frequency)

n = length(f);

k = 1:1:2000; %range of wavenumbers
for j =1:n
    w(j)= 2*pi*f(j);     % angular frequency
    H = (3.175e-3) / 2; % m    (plate thickness)
    k1(j) = w(j)/c1;   % wavenumber
    k2(j) = w(j)/c2;
  
    for i = 1:length(k)
        n_1(j) =  sqrt((i)^2-k1(j)^2);
        n_2(j) =  sqrt((i)^2 - k2(j)^2);
        f1(i,j) = (((2* (i)^2 - (k2(j))^2)^2)*(sinh(n_1(j)*H)*cosh(n_2(j) *H))-(4*(i)^2 * n_1(j) * n_2(j)*cosh(n_1(j)*H)*sinh(n_2(j) *H))); %function
        % f2(i) = (((2* i^2 - (k2(j))^2)^2)*(cosh(n_1*H)*sinh(n_2 *H))-(4*i^2 * n_1 * n_2*sinh(n_1*H)*cosh(n_2 *H)));
        
    end
end
%% Root finding methods (Secant method)
% f1 antisymmetric function kg is the root 

kg1 = 21;
kg2 = 50;
eps = 0.1;

for j = 1:750
    i = 2;
    while abs(f1) > eps
        i = i + 1;
        kg(i) = kg(i-1) - (f1(kg(i-1))*(kg(i-1) - kg(i-2))) / (f1(kg(i-1))-f1(kg(i-2)));
    end
    root1 = kg(end);
    if i > 2 
        kg(2) = kg(1);
        kg(end) = kg(2);
    end
end