Identifying parameters for an Equation of motion

Hi, I have a data set that represent the free vibration of a structure. I want to quantify the dynamic parameters of the structure (mass, stiffness, damping coefficient, friction force) using optimization scheme by solving an equation of motion, which defined as follows:

What I am try to do is how to define the objective function that I want to pass it to the optimizing function (ga:genetic algorithm). I wort so far a function that will give me the difference( that I want to minimize it) between two curves (data set and the solution of the equation for specified conditions and values of the parameters that I want to quantifying them (m, k, c*, F). What I am stuck on is how to define these parameters as variables that I am seeking for in the optimizing function (ga).

• my main script:*

% define the initial conditions and parameters
initial=[30/1000, 0]; % [displacement Velocity]
m=2459;k=107178;zeta=.05;
F=300;
dt=0.02;
tf=10;
% define the data set
d2=........;
% call the function that will solve the equation and return the difference between the two curves. I used Runge-Kutta method
f=RK(k,m,zeta,F,initial,dt, tf,d2,h)

_ * * My function**_

function C1= RK(k,m,zeta,F,initial,dt, tf,d2,h)

for i=1:length(t)-1

    %   here the Rk implementation script  ;

end

d1=........;   % the computed displacement response for specific parameters 
h=length(d1);

1 %%%%%simple difference

diff=abs((d2(1:h))-(d1)');
C1 =sum(diff);

So for one special initial condition, I want to vary the parameters values until I get the global optimum set of parameters that gives me the minimum difference between the two curves. Any ideas? Would anyone help me,please!

Thanks