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dassl
From: 
John W. Eaton 
Subject: 
dassl 
Date: 
Fri, 19 Jun 1998 00:08:11 0500 (CDT) 
On 18Jun1998, address@hidden <address@hidden> wrote:
 this is some question relating dassl. I've formulated a simple
 differentialalgebraic problem. At a singularity, dassl crashes
 and leaves octave completely. So I end up with the following
 question:

 How can such a crashing be avoided? (Perhaps there is a bugfix
 that at least helps to gracefully return to the interpreter)
I posted a patch a few weeks ago that fixes this bug. It's available
from http://www.che.wisc.edu/octave/mailinglists/bugoctave/1998/243.
 Anyway, I tried to set the following hint from the handbook into operation:

 "The fifth argument {to dassl} is optional, and may be used to
 specify a set of times that the DAE solver should not integrate
 past. It is useful for avoiding difficulties with singularities and
 points where there is a discontinuity in the derivative."

 But I failed because I didn't find any example of how to specify
 a set of times that the DAE solver should not integrate past.
With the patch, your example doesn't crash Octave, but it still
fails. However, I don't think the bug is in Octave. With different
initial derivaties, it seems to work fine. For example, both of the
following calls to dassl succeed (though the second is probably
better, since it forces dassl to restart at t == 8).
function res = f(x,xdot,t)
res(1) = xdot(1)x(2);
res(2) = 16  x(1)  sign(x(2)) * x(2) * x(2);
end
p = dassl ("f", [0;4], [0;0], t=linspace (0, 100)');
p = dassl ("f", [0;4], [0;0], t=linspace (0, 100)', 8);
jwe