system of nonlinear differential equations

I have two systems of nonlinear equation. I need to solve this equation with matlab.I'm searching in the internet but culdn't find the solution could you help me pls? equations are: http://d1204.hizliresim.com/w/k/4kn5l.png

[osman]

only theta and x are variable

[osman]

any suggestion

[Walter Roberson]

Do the dots indicate differentiation?

If only theta and x are variable, but you are differentiating theta and x, then what are you differentiating them with respect to? Are you sure they are variables and not functions such as x(t) and theta(t) with differentiation with respect to t ?

Answer 1

[osman]

function turev = derivati( t,h )

M_ball=0.0327;
g=9.8;
J_bm=0.0620;
K=4.9100;
Ke=4.77;
R=4.7;
Rb=0.01;
b=1.5279;
a1=0.0050;
V=1;
% h1=theta
% h2=Dtheta
% h3=x
% h4=Dx
% turev1=Dtheta
% turev2=D2theta
% turev3=Dx
% turev4=D2theta
turev=zeros(size(h));
   turev(1) = h(2);
   turev(2) = (K/(R*J_bm)*V)-(K*Ke/R+b)/J_bm*turev(1)-h(3)*M_ball/J_bm*g*cos(h(1));
   turev(3) = h(4);
   turev(4) = g*sin(h(1))/(1+(2/5)*(Rb/a1)^2);

end

this is my answer and it works. this may help somebody