From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 23343 invoked by alias); 17 Mar 2008 13:47:45 -0000 Received: (qmail 23327 invoked by uid 22791); 17 Mar 2008 13:47:44 -0000 X-Spam-Check-By: sourceware.org Received: from dns2.synchrotron-soleil.fr (HELO raclette.synchrotron-soleil.fr) (195.221.0.6) by sourceware.org (qpsmtpd/0.31) with ESMTP; Mon, 17 Mar 2008 13:47:18 +0000 Received: from localhost (unknown [127.0.0.1]) by raclette.synchrotron-soleil.fr (Postfix) with ESMTP id 992203010E for ; Mon, 17 Mar 2008 13:40:57 +0000 (UTC) Received: from raclette.synchrotron-soleil.fr ([127.0.0.1]) by localhost (raclette.synchrotron-soleil.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id giLsxqohaWac for ; Mon, 17 Mar 2008 14:40:47 +0100 (CET) Received: from venus.synchrotron-soleil.fr (venus.synchrotron-soleil.fr [195.221.0.131]) by raclette.synchrotron-soleil.fr (Postfix) with ESMTP id 4865B3098B for ; Mon, 17 Mar 2008 14:40:39 +0100 (CET) Received: from lune1.synchrotron-soleil.fr ([195.221.0.153]) by venus.synchrotron-soleil.fr with Microsoft SMTPSVC(6.0.3790.1830); Mon, 17 Mar 2008 14:46:44 +0100 Received: from localhost.localdomain ([195.221.5.120]) by lune1.synchrotron-soleil.fr with Microsoft SMTPSVC(6.0.3790.3959); Mon, 17 Mar 2008 14:46:44 +0100 Date: Mon, 17 Mar 2008 13:47:00 -0000 From: picca To: gsl-discuss@sourceware.org Subject: nmsimplex iteration. Message-ID: <20080317144641.332eb83a@synchrotron-soleil.Fr> X-Mailer: Claws Mail 3.3.1 (GTK+ 2.12.5; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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-q1/txt/msg00036.txt.bz2 Hello I am using the simplex minimisation to solve a problem of crystallography. The function to minimize is : f = f(euler_x, euler_y, euler_z, a, b, c, alpha, beta, gamma); in fact a, b, c, alpha, beta, gamma are the parameters of a triedra, a, b, c, are the length of the sides and alpha, beta, gamma the angles of the triedra. for some combinations of alpha, beta, gamma , f(blabla...) = GSL_NAN. So the simplex can not converge. If I return a really big number as it was suggested in a previous thread of the mailing list, the simplex must be contracted around the better corner. But it is not always possible to obtain a valid contraction in one guess. To be clear this simplex algorithm only work for a convex space. And my problem is not convex. Nevertheless if we are close enough of the solution, the problem become locally convex. To achieve this, we must contraction the simplex till it becomes valid. Is it possible to tune the simplex algorithm to solve also those locally convex problems. Another problem is that the initial guest of the simplex is not always possible. Can I create by myself the starting points of the simplex ? Frederic