The function dinamica expects 6 input arguments. However, the function, f that ode45 takes as input is handled as a function of two input arguments, so inside ode45 that function is called like this:
dydt = f(t,y);
Then inside your dinamica it crashes because it is expecting the 6 inputs. You have to change the call to something like this:
[t,x_sp]=ode45(@(t,x) Dinamica(t,x,a,b,c,x_in),[0 20],[0 0]);
However, inside dinamica you have a multiplication with the entire x_in array, that is every value of something you claim to be something varying harmonically. That will not work. You have to estimate the value of x_in at the time t. To do that you can do something like this:
function dx_sp=Dinamica(t,x_sp,a,b,c,t_in,x_in)
u=x_sp(1);
v=x_sp(2);
x_in_at_t = interp1(t_in,x_in,t,'pchip');
dx_sp=(x_in_at_t*a*b^2)-(2*c*b*v)-(u*b^2);
end
and change the call to:
[t,x_sp]=ode45(@(t,x) Dinamica(t,x,a,b,c,t_in,x_in),[0 20],[0 0]);
HTH
