Please help me in completing this program?

function du=mydiff(tau,u)
tau= 1:20;
for tau=1:20
    u(tau)=1;
end
b=4.5;          %backlash,2b=9 micro metre
Z1=62;          %no. of teeth in  Gear
Z2=42;          %no. of teeth in Pinion
T1=7640;        %torque of Gear in N-mm
N1=5000;        %Speed of Gear in rpm
M1=11.815;      % mass of gear in kg
M2=5.357;       %mass of pinion in kg
I1=37257;       %inertia of Gear in kg-mm2
I2=82103;       %inertia of pinion in kg-mm2
me=2.279;       %mass equivalent in kg
km=2.3426e7;    %average stiffness in N/m
Fm=105;         %total Normal force in N
omega0=sqrt(km/me);             % frequency of gear pairin rad/sec
omegae=(2*pi*Z1*N1)/60;         %natural frequency in rad/sec
ohm=omegae/omega0;              % frequency ratio
F0=0.4482;                      %Dimensionless load=(Fm/me*l*omega0^2)
zeta=0.06;                      %damping ratio
t=[];
%f(u(tau)) Dimensionless nonlinear gap function
tau=omega0*t;                   %Dimensionless time
l=1e-6;                         %characteristic length
q(t)=l*u(tau);
thetaj=0;
kj=[23.5396 3.5448 0.8489 0.5454 .0302 0.5012]*10^6;
kbn=kj/km;
ej=[20 3.45 0.26 .45]*10^-6;
ejb=ej/l;
for tau=1:20
    if(u(tau)>b/l)
        f(u(tau))=u(tau)-b/l;
    end
    if(u(tau)> -b/l && u(tau)<b/l)
        f(u(tau))=0;
    end
    if(u(tau)<-b/l)
        f(u(tau))=u(tau)+b/l;
    end
end
for n= 1 :5
    sum1=kbn*cos(n*ohm*tau)*f(u(tau));
end
sum1=sum1+1;
for j=1:5
    sum2=ejb*j*j*cos((j*ohm*tau)+thetaj);
end

du(1) = u(2); 
du(2) = F0+(ohm*ohm*sum2)-sum1-(2*zeta*u(2));
du = [du(1); du(2)];

[tau,u] = ode15s('mydiff', [0 25], [1 1]); 
plot(tau,u(:,1))

whats wrong with this program?

[Walter Roberson]

1. there is no indication of its purpose.
2. there is no description of the problem being encountered

[ravishankar]

Actually i have a 2nd order non-linear ordinary differential equation i.e. u double dot(tau)+(2*zeta*u dot(tau))+(1+summation from n=1 to infinity (kbn*cos(n*ohm*tau)))=F0+(ohm^2*summation from j=1 to infinity *j^2*ejb*cos(j*ohm*tau+thetaj)) where tau -dimensionless time=omega0*time

by using Runge kutta method to solve 2nd order diff eq.,i have converted a 2nd order to 1st order. I want phase plane diagrams,dispacement/vel/acc vs time,poincare maps.

Answer 1

[Image Analyst]

3. There are no comments after the initialization comments. No comments about what the loops and ode15s are supposed to do.

4. No initialization of du early in the function so that an error in the program will throw an additional, secondary error about du not being assigned.

5. This code:

tau= 1:20;
for tau=1:20
    u(tau)=1;
end

can be replaced by this:

u = ones(1, 20);

6. Since u is 1 for any tau, this code probably does not do what you expect:

if(u(tau)>b/l)
        f(u(tau))=u(tau)-b/l;
    end
    if(u(tau)> -b/l && u(tau)<b/l)
        f(u(tau))=0;
    end
    if(u(tau)<-b/l)
        f(u(tau))=u(tau)+b/l;
    end

You're basically setting f(1) to something.

On the plus side though, you did explain the initial variables and eve gave their units. (Don't know what "pairin" means though.)