Re: Help need for Differential algebraic equations

[genehacker]

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;

x0 = [100,0,0];
xdot0 =[-10,10,10];
t = linspace(0,50,50);
[x,xdot] = 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 =    1.425756E-11  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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