Re: System of differential-algebraic equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg78310] Re: System of differential-algebraic equations*From*: dh <dh at metrohm.ch>*Date*: Thu, 28 Jun 2007 04:21:34 -0400 (EDT)*References*: <f5tbnq$24q$1@smc.vnet.net>

Hi Jose, your system is not consistent. E.g. the initial conditions do not fullfill the first equation. hope this helps, Daniel José Luis Gómez wrote: > Dear Mathematica Group. > > > > A colleague has asked me help to solve a system of 8 algebraic and > differential equations. The system is included below, at the end of this > e-mil, in InputForm. > > Mathematica 6.0 NDSolve command replies with this message: > > > > NDSolve::icfail: Unable to find initial conditions which satisfy the > residual function within specified tolerances. Try giving initial > conditions for both values and derivatives of the functions. > > > > Now, my colleague does not want to give initial conditions for the > derivatives, because he does not have actual information about those values. > We fool around a bit in the documentation, play a little bit with > AccuracyGoal, and PrecisionGoal, and with different methods specified by > Method, but we were not able to obtain an answer. > > > > Does anyone have a suggestion for us? Can we avoid the use of initial values > for the derivatives? > > > > The system is included below. Thanks in advance for any advice. > > > > Jose Luis Gomez-Munoz > > > > > > > > NDSolve[{m[t]*x[t] + q[t]*x[t]^2 == 2.75, > > (12.6/10^15)*m[t]^2 - (10.2/10^16)*m[t]*r[t] - > > (20.4/10^16)*m[t]*u[t]*y[t] + (20.4/10^16)*m[t]*u[t]*x[t] - > > (92.4084/10^15)*q[t] == 0, > > r[t]*(y[t] - x[t]) + u[t]*(y[t] - x[t])^2 == 0.444, > > (10.2/10^16)*r[t]^2 - (9.82/10^12)*r[t]*v[t] - > > (389.9256/10^16)*u[t] == 0, v[t] + 2*w[t]*(y[t] - 140/10^16) == > > 0, 0.5*Derivative[1][m][t]*x[t]^2 + > > m[t]*x[t]*Derivative[1][x][t] + (1/3)*DerivaFrom - Wed Jun 27 14:38:12 2007 X-Account-Key: account2 X-UIDL: GmailId1136cf3febdca013 X-Mozilla-Status: 0009 X-Mozilla-Status2: 00000000 X-Mozilla-Keys: Delivered-To: sunfreeware at gmail.com Received: by 10.114.59.14 with SMTP id h14cs190705waa; Wed, 27 Jun 2007 04:32:18 -0700 (PDT) Received: by 10.100.47.9 with SMTP id u9mr217337anu.1182943936184; Wed, 27 Jun 2007 04:32:16 -0700 (PDT) Return-Path: <steve at localhost.twtelecom.net> Received: from localhost.twtelecom.net (66-193-208-83.static.twtelecom.net [66.193.208.83]) by mx.google.com with ESMTP id b11si11398641ana.2007.06.27.04.31.58; Wed, 27 Jun 2007 04:32:16 -0700 (PDT) Received-SPF: pass (google.com: domain of steve at localhost.twtelecom.net designates 66.193.208.83 as permitted sender)