From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: ODE stiffness problems
Date: Fri, 15 Mar 2013 08:54:07 +0000 (UTC)
Organization: The MathWorks, Inc.
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"Matthew" wrote in message <khtlea$ba3$>...
> I removed the abs and signs by putting a constant low flow rate just to see if it would work. However it doesn't make any change it still stops at the same point.

I solved your problem with another software and it worked without problems.

The problem with ODE15s seems to be the abrupt change of the variables
in the time span from t=0.95 to t=1. This is caused by the parameter Av.

A remedy (I also used within my ODE integrator) is to call ODE15s seperately for 
the time span from t=0 to t=0.05, then from t=0.05 to t=0.95 and then from t=0.95 to t=1.  
Do it in a loop and set the inital conditions of the variables for a new time span to the final values of the variables from the preceeding time span.

Best wishes