Path: csiph.com!fu-berlin.de!uni-berlin.de!news.dfncis.de!not-for-mail From: =?UTF-8?Q?Hans-Bernhard_Br=c3=b6ker?= Newsgroups: comp.graphics.apps.gnuplot Subject: Re: What's new in gnuplot 5.2 Date: Mon, 5 Jun 2017 14:47:35 +0200 Lines: 23 Message-ID: References: <022e551d-f7c4-44a1-973b-f8db0375854b@googlegroups.com> <91f133a9-ec73-423a-fb72-de13397f48aa@t-online.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: news.dfncis.de uv14Z6Z47Do0/R1lc5Cg9AHPnc2T1WSNPrcscsJ8Br47NAetzhEh9r4FJt Cancel-Lock: sha1:s4kEbX2d8mHmFBP0LCaR7FaN/+M= User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 In-Reply-To: Content-Language: de-DE Xref: csiph.com comp.graphics.apps.gnuplot:3670 Am 05.06.2017 um 10:32 schrieb hugocoolens@gmail.com: > Op zaterdag 3 juni 2017 22:45:42 UTC+2 schreef Hans-Bernhard Bröker: >> Often the function can be transformed a bit to lift such requirements. >> In this case, you could just fit >> >> f(x) = 10 * log10(a**2 / (1 + (x / b)**2)) >> >> or >> >> f(x) = 20 * log10a - 10 * log10(1 + (x / b)**2) \ > thank you very much for your help, I tried out > f(x) = 20 * log10a - 10 * log10(1 + (x / b)**2) but that didn't make > any difference. However f(x) = 10 * log10(a**2 / (1 + (x / b)**2)) does make a difference but "a" still becomes negative for certain fitting intervals. Part of the trick is that this doesn't actually matter. The function is identical for parameters a and -a, so you can just throw away the sign afterwards. The requirement that a be positive was an artificial one from the beginning.