plotting nonlinear system with constant input

I want to plot nonlinear system,I enter function in M-file like that:

function dx=suspension(t,x,Mb,Mf,Mr,I,Ksf,Ksr,Ktf,Ktr,Csf,Csr,Lf,Lr,Wf,Wr)
Mb=730;Mf=40;Mr=36;I=1230;Ksf=19960;Ksr=17500;Ktf=175500;Ktr=175500;
Csf=1290;Csr=1620;Lf=1;Lr=(1.8);Wf=0.05;Wr=0.05;
dx=zeros(8,1);
%Wf and Wr is constant input  as road bump
dx=[x(5);x(6);x(7);x(8);1/Mb*((-Ksf-Ksr)*x(1)+Ksf*x(2)+Ksr*x(3)-Lf*Ksf*sin(x(4))+Lr*Ksr*sin(x(4))-Lf*Csf*x(8)*cos(x(4))+Lr*Csr*x(8)*cos(x(4))-(Csf+Csr)*x(5)+Csf*x(6)+Csr*x(7));1/Mf*(Ksf*x(1)-(Ksf+Ktf)*x(2)+Lf*Ksf*sin(x(4))+Lf*Csf*x(8)*cos(x(4))+Csf*x(5)-Csf*x(6)+Ktf*Wf); 1/Mr*(Ksr*x(1)-(Ksr+Ktr)*x(3)-Lr*Ksr*sin(x(4))-Lr*Csr*x(8)*cos(x(4))+Csr*x(5)-Csr*x(7)+Ktr*Wr);
1/I*((-Lf*Ksf+Lr*Ksr)*x(1)+Lf*Ksf*x(2)-Lr*Ksr*x(3)-Lf*Lf*Ksf*sin(x(4))-Lr*Lr*Ksr*sin(x(4))-Lf*Lf*Csf*x(8)*cos(x(4))-Lr*Lr*Csr*x(8)*cos(x(4))-(Lf*Ksf-Lr*Csr)*x(5)+Lf*Csf*x(6)-Lr*Csr*x(7))];
y=[x(2);x(3)];%output

>>[t,y]=ode45('suspension',[0 10],[0;0;0;0;0;0;0;0]);

>>plot(t,y(:,1));

is it true for my task?thank you

Answer 1

[Walter Roberson]

No, that is not correct, or at least it is not clear. Please read http://www.mathworks.com/help/techdoc/math/bsgprpq-5.html

[Eka]

what must I do to make the equation is correct?n how I declare function of 'x' or dimension of 'x'?thank you

[Walter Roberson]

function dx = suspension(t, x, Mb, Mf, Mr, I, Ksf, Ksr, Ktf, Ktr, Csf, Csr, Lf, Lr, Wf, Wr)

    dx = zeros(8,1);

    %Wf and Wr is constant input  as road bump

    dx = [ x(5);
           x(6);
           x(7);
           x(8);
           1/Mb * ((-Ksf-Ksr) * x(1) + Ksf * x(2) + Ksr * x(3) - Lf * Ksf * sin(x(4)) + Lr * Ksr * sin(x(4)) - Lf * Csf * x(8) * cos(x(4)) + Lr * Csr * x(8) * cos(x(4)) - (Csf + Csr) * x(5) + Csf * x(6) + Csr * x(7));
           1/Mf * (Ksf * x(1) - (Ksf + Ktf) * x(2) + Lf * Ksf * sin(x(4)) + Lf * Csf *x(8) * cos(x(4)) + Csf * x(5) - Csf * x(6) + Ktf * Wf);
           1/Mr * (Ksr * x(1) - (Ksr + Ktr) * x(3) - Lr * Ksr * sin(x(4)) - Lr * Csr * x(8) * cos(x(4)) + Csr * x(5) - Csr * x(7) + Ktr * Wr);
           1/I * ((-Lf * Ksf + Lr * Ksr) * x(1) + Lf * Ksf * x(2) - Lr * Ksr * x(3) - Lf * Lf * Ksf * sin(x(4)) - Lr * Lr * Ksr * sin(x(4)) - Lf * Lf * Csf * x(8) * cos(x(4)) - Lr * Lr *Csr * x(8) * cos(x(4)) - (Lf * Ksf - Lr * Csr) * x(5) + Lf * Csf * x(6) - Lr * Csr * x(7)) ];

    y = [x(2); x(3)]; %output

end

And to invoke it,

Mb=730; Mf=40; Mr=36; I=1230; Ksf=19960; Ksr=17500; Ktf=175500; Ktr=175500; Csf=1290; Csr=1620; Lf=1; Lr=(1.8); Wf=0.05; Wr=0.05;

objfun = @(t,x) suspension(t, x, Mb ,Mf, Mr, I, Ksf, Ksr, Ktf, Ktr, Csf, Csr, Lf, Lr, Wf, Wr);

[t,y]=ode45(objfun, [0 10], [0;0;0;0;0;0;0;0]);

Note though that your assignment to "y" inside "suspension" is not doing anything useful. "y" is a local variable there, and its value is not being used to create any output argument, so the value of "y" will be discarded once the function ends.

I made no attempt to examine the mathematics of your "dx" calculation. You did not indicate the system of ODE's that you are working with, so all I can do is examine the syntax of the calculation. The changes I made to "suspension" itself are cosmetic, but necessary if one is to have any realistic hope of figuring out what it is doing. Whitespace is important in programming!!

[Eka]

after running, your code with mine is same,and the figure of simulation before and after linearization nothing difference...what's wrong with this function?

I got equation above from a half suspension system and I give the road bump disturbance as high as 5 cm, what must I do to run the program with nothing error?yhank you