Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!goblin2!goblin.stu.neva.ru!feeder.erje.net!newsfeed.kamp.net!newsfeed.kamp.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Ingo Thies Newsgroups: comp.graphics.apps.gnuplot Subject: Re: Wrong fit direction / zrange / unreadable graph file Date: Thu, 19 May 2011 10:58:12 +0200 Lines: 24 Message-ID: <93k4d4Ft5iU1@mid.individual.net> References: <01ac512a-8031-41f0-a899-0684927f6c32@n10g2000yqf.googlegroups.com> <93c9dhFmvmU1@mid.individual.net> <93j3kjFts6U1@mid.dfncis.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Trace: individual.net fj22d+oOvYK/7QuP3Dv9lQ6Da90QtU7s2lQmeBthS7AxIuCNZa Cancel-Lock: sha1:8LAQctbWU/bHvhnv39g2dCxA960= User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10 In-Reply-To: <93j3kjFts6U1@mid.dfncis.de> Xref: x330-a1.tempe.blueboxinc.net comp.graphics.apps.gnuplot:326 On 19.05.2011 01:39, Hans-Bernhard Bröker wrote: > gnuplot's fit model isn't linear, though. I.e. "fit" doesn't assume, > nor does it know, whether the model function is a straight line. As far > as gnuplot is concerned, the model is an arbitrarily complicated > function of one variable and two parameters. Gnuplot doesn't have to assume that a linear function is to be fitted since the user already provides its form: f(x)=a+b*x fit [rangeinfo] f(x) via a,b So, no reason for f(x) to behave in a strange way for a=0, or to assume anything else then exactly the type of function the user is requesting for. And, as mentioned, there are standard Levenberg-Marquardt algorithms which do not stumble over that. Therefore, I would guess, that the problem is caused by the implementation into gnuplot rather than by the method itself. -- Gruß, Ingo