Path: news.mathworks.com!newsfeed-00.mathworks.com!newsfeed2.dallas1.level3.net!news.level3.com!postnews.google.com!k6g2000vbz.googlegroups.com!not-for-mail From: <HIDDEN> Newsgroups: comp.soft-sys.matlab Subject: Re: DAE in matlab Date: Tue, 7 Feb 2012 03:26:58 -0800 (PST) Organization: http://groups.google.com Lines: 35 Message-ID: <a9609639-aa4e-4e22-a43b-4bc6b30e69e5@k6g2000vbz.googlegroups.com> References: <jgp3bm$21n$1@newscl01ah.mathworks.com> <jgp7s2$i8i$1@newscl01ah.mathworks.com> <jgqufj$99r$1@newscl01ah.mathworks.com> NNTP-Posting-Host: 192.102.151.35 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1328614110 11307 127.0.0.1 (7 Feb 2012 11:28:30 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 7 Feb 2012 11:28:30 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: k6g2000vbz.googlegroups.com; posting-host=192.102.151.35; posting-account=X3eThQoAAACh5vOSip_rNRzKAq7k0jPW User-Agent: G2/1.0 X-Google-Web-Client: true X-Google-Header-Order: ARLUEHNKC X-HTTP-UserAgent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E),gzip(gfe) Xref: news.mathworks.com comp.soft-sys.matlab:756978 On 7 Feb., 11:30, "Michal Lukac" <michal.lu...@fstroj.uniza.sk> wrote: > > A couple of questions: In the notation "x4.b.sin(x1-pi)" I assume the dot indicates multiplication, so why isn't it used in for example "x3cos(x2)"? Also why write "sin(x1-pi)" instead of "-sin(x1)"? > > Yes, You are right the dot are multiplications, I wanted to write the equations more readable.... and hasn't crossed my mind to simplify the expressions.... sorry. > These equations describe motion of a mechanism. I wrote them as I derive them from the drawing of mechanism. The last two eq. are constrains of the mechanism. > > I tried to use ode15i, odebim(I have found here), but unsecesfull. I'm not a mathematician... These equationas are DAE differential equations + algebraic equations.http://en.wikipedia.org/wiki/Differential_algebraic_equation > > I have' found something about index of DAE, but i don't understand well and the solvers solve the equations just of particular index. > May be, I need to modify these euations a bit but I don't know how.. > When I tried to use ode15i and odebim I reduced the order of DE by substitutions > d_y1 = dd_x, d_y2 = d_x, ...etc... > > thanks. There are specialized codes for the simulation of constraint mechanical systems. Take a look at the 'Mechanical Systems' section under http://www.unige.ch/~hairer/software.html I doubt that MATLAB's ode15i can handle index-2 systems as it is required for your set of equations. Best wishes Torsten.