What's the alternative of ode45 function ?

Hi, i have done this function to resolve a second order differential equation but i want to fix the time as a constant equal to 10 by changing the ode45 by another function:

function xdot = equacte(t,x,rload)

% Function file for mass with spring.

% Position is first variable, velocity is second variable,load is the third variable

freq=100;

w=2*pi*freq;

m=0.0112;

k=279.9919 ;

teta =-7.3333e+03;

cp= 1.8492*10^-7;

A = [0,1,0;-k/m,0,-teta/m;(-teta/rload),0,-1/(rload*cp)];

B = [0;1/m;0];

f =sin(w*t);

xdot = A*x+B*f;

end

Then in principle program:

rload=5000;

[t,x]=ode45(@(t,x) equacte(t,x,rload),[0:0.000001:5],[0,0,0]);

Answer 1

[Sebastian Castro]

How about this:

http://www.mathworks.com/matlabcentral/answers/98293-is-there-a-fixed-step-ordinary-differential-equation-ode-solver-in-matlab-8-0-r2012b

Keep in mind that the variable-step ode45 may be taking much smaller time steps to keep the integration error down. With a fixed-step solver, you have no guarantees of meeting error tolerances and your sample time will have to be carefully chosen.

- Sebastian

[Mallouli Marwa]

No i have this error Undefined function or variable 'ode4'.

Error in bimorphnew (line 36)

[t,x]=ode4(@(t,x) equacte(t,x,rload),tspan,[0,0,0]);

[Sebastian Castro]

Yeah, could't guarantee that the ZIP file in the Answer would work given that was made for R2012b...

Simulink has built-in fixed-step solver support. If you have Simulink, you can fairly easily translate your model using a State-Space block, given that your model is fully linear.

- Sebastian

[Mallouli Marwa]

No i haven't simulink. Can i use lsim as a relative of ode45 and how ? Please help me

[Sebastian Castro]

That might work. You could get away with discretizing the system to your sample rate of 10 using c2d and then passing it in to lsim. According to the documentation,

Discrete-time systems are simulated with ltitr (state space) or filter (transfer function and zero-pole-gain).

- Sebastian