Path: news.mathworks.com!not-for-mail 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. Lines: 15 Message-ID: <khunje$be2$1@newscl01ah.mathworks.com> References: <khqcg9$anl$1@newscl01ah.mathworks.com> <khs33m$h41$1@newscl01ah.mathworks.com> <kht2it$atg$1@newscl01ah.mathworks.com> <khtlea$ba3$1@newscl01ah.mathworks.com> Reply-To: <HIDDEN> NNTP-Posting-Host: www-01-blr.mathworks.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: newscl01ah.mathworks.com 1363337647 11714 172.30.248.46 (15 Mar 2013 08:54:07 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Fri, 15 Mar 2013 08:54:07 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 3799640 Xref: news.mathworks.com comp.soft-sys.matlab:791214 "Matthew" wrote in message <khtlea$ba3$1@newscl01ah.mathworks.com>... > 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 Torsten.