Re: Help need for Differential algebraic equations

[genehacker]

thanks very much for the help. now it defnitely works:)



genehacker wrote:
> 
> Hi all,
>  
>     I am new to octave and i love it the best as an open source
> alternative to matlab. I used lsode to solve ordinary diff equations, but
> now I do also have some algebraic equations to solve along.
> 
> I came across this function 'dassl', which is supposed to solve
> differential algebraic equations, but have problems using it. This is how
> i use it currently and below is the error message. I have no idea what it
> is. Please help!
> 
> ******code*****
> 
> function xdot = f(x,xdot,t);
> %define all parameter values viz. k12, k23,f86 etc here
> xdot = zeros(9,1);
> xdot(2) = k12*x(1) - k23*x(2);
> xdot(3) = k23*x(2);
> xdot(5) = k45*x(4) - k56*x(5);
> xdot(6) = k56*x(5) - k67*x(6);
> xdot(7) = k67*x(6);
> 
> x(8) = f86*x(6);
> x(9) = f29*x(2);
> endfunction;
> 
> 
> x0 = ones(9,1)';
> xdot0 =zeros(9,1)';
> t = linspace(0,50,50);
> dassl("f",x0,xdot0,t)
> 
> *****output******
> 
>  ***MESSAGE FROM ROUTINE DDASSL IN LIBRARY SLATEC.
>  ***POTENTIALLY RECOVERABLE ERROR, PROG ABORTED, TRACEBACK REQUESTED
>  *  AT T =    0.000000E+00  AND STEPSIZE H =    1.594388E-05  THE
> ITERATION
>  *  MATRIX IS SINGULAR
>  *  ERROR NUMBER = -8
>  *
>  ***END OF MESSAGE
> 
>  ***JOB ABORT DUE TO UNRECOVERED ERROR.
> 0          ERROR MESSAGE SUMMARY
>  LIBRARY    SUBROUTINE MESSAGE START             NERR     LEVEL     COUNT
>  SLATEC     DDASSL     AT T =    0.000000E+        -8         1         1
> 
> error: exception encountered in Fortran subroutine ddassl_
> error: caught execution error in library function
> 

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