Re: Help need for Differential algebraic equations

[John W. Eaton]

On  9-Oct-2008, genehacker wrote:

| 
| Thanks for the reply Olaf. I defnitely changed the function return variable,
| that should be different from xdot. But i still have a problem of running a
| simple differential algebraic equation. I am getting the same answer, if i
| tried a much simpler set of equations(even though I didnot use an algebraic
| equation here, I intend to use it later on). [ Also, you asked why I am
| doing x(2) = f*x(6), thats is the type of algebraic equation i intend to
| use]. Is there something inherently wrong with my code? I couldnot get much
| help about this online.
| 
| **********code ********
| function res = f(x,xdot,t);
| res = zeros(3,1);
| k12=0.1;
| k23=0.7;
| 
| xdot(1) = -k12*x(1);
| xdot(2) = k12*x(1) - k23*x(2);
| xdot(3) = k23*x(2);
| 
| endfunction;

X nad XDOT are parameters to your function.  Changing them has no
effect.  If you are solving a DAE with dassl, you should be defining a
residual funtion F such that it computes RES as a function of X, XDOT,
and T.  Your function above simply sets RES to zero.

If your function is as you show above, then it looks like an ODE, not
a DAE.

jwe