Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2007
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2007

[Date Index] [Thread Index] [Author Index]

Search the Archive

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)


  • Prev by Date: Re: Mathematica code for survival functions
  • Next by Date: Re: Why use Java in Mathematica?
  • Previous by thread: System of differential-algebraic equations
  • Next by thread: Re: System of differential-algebraic equations