Re: Octave code for y'''=0 ODE

[Doug Stewart]

On Tue, Jul 28, 2015 at 4:51 AM, deepus <address@hidden> wrote:

How can I write in this format

/function ret=f(x,t); ret=2*t^2; end;
x=lsode('f',3,(t=linspace(0,3,4)));
#plot(t,x)
x/

---
[this is an example octave code for first degree ODE]
Your answer is really helpful, but am little confused how/where to start.
Please help me..



-

This uses the symbolic package to solve a 2nd order system

It might help!!

## This is a demo of a second order transfer function and a unit step input.

 ## in laplace we would have        1                       1

 ##                              _______________         *  _____

 ##                             s^2 + sqrt(2)*s +1           s

 ##

 ## So the denominator is s^3 + sqrt(2) * s^2 + s

 # and for laplace initial conditions area

 ##             t(0)=0 t'(0) =0  and the step has initial condition of  1

 ## so we set   t''(0)=1

 ## In the code we use diff(y,1)(0) == 0 to do t'(0)=0

 ##

 ## I know that all this can be done using the control pkg

 ## But I used this to verify that this solution is the

 ##   same as if I used the control pkg.

 ## With this damping ratio we should have a 4.321% overshoot.

 ##

 syms y(x) 

 de =diff(y, 3 ) +sqrt(2)*diff(y,2) + diff(y) == 0;

 f = dsolve(de, y(0) == 0, diff(y,1)(0) == 0 , diff(y,2)(0) == 1)

 ff=function_handle(rhs(f))

  x1=0:.01:10;

 y=ff(x1);

 plot(x1,y)

 grid minor on 

--

DAS