From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28387 invoked by alias); 3 Sep 2008 10:58:12 -0000 Received: (qmail 28372 invoked by uid 22791); 3 Sep 2008 10:58:11 -0000 X-Spam-Check-By: sourceware.org Received: from mail.network-theory.co.uk (HELO mail.network-theory.co.uk) (66.199.228.187) by sourceware.org (qpsmtpd/0.31) with ESMTP; Wed, 03 Sep 2008 10:57:30 +0000 Date: Wed, 03 Sep 2008 10:58:00 -0000 Message-ID: From: Brian Gough To: Tuomo Keskitalo Cc: gsl-discuss@sourceware.org Subject: Re: GSL ode-initval development In-Reply-To: <48BA4766.6070701@iki.fi> <48BD8EF0.5030502@iki.fi> References: <48A7E377.3020607@iki.fi> <48BA4766.6070701@iki.fi> User-Agent: Wanderlust/2.14.0 (Africa) Emacs/22.2 Mule/5.0 (SAKAKI) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII X-Message-Mac: 92da46eeb502187970ae0b19418cc6c8 Mailing-List: contact gsl-discuss-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gsl-discuss-owner@sourceware.org X-SW-Source: 2008-q3/txt/msg00024.txt.bz2 At Sun, 31 Aug 2008 10:25:26 +0300, Tuomo Keskitalo wrote: > I have been writing a non-linear equation solver based on a modified > Newton iteration method, and a question about failures has come up. What > value should the non-linear equation solver return to the stepper (and > from there to user) in the case that the method reaches a maximum number > of Newton iterations and therefore fails? GSL_CONTINUE or GSL_FAILURE or > something else? I'd suggest GSL_FAILURE to start with. Hopefully the solver won't fail that often. > which values of variables y should a stepper which uses step doubling > for error estimation return: The values from the single step or the > values from two half steps? You would expect to get the values of single > step from "a stepper", but the values from two half steps should be more > accurate, and they are available. The final value of y should come from the two half steps as they are more accurate. See rk4.c for an example and the error estimate. -- Brian Gough