The GSL Bugs Database is at http://savannah.gnu.org/bugs/?group=gsl This file was generated from it at Thu Jul 18 10:23:38 2013 ------------------------------------------------------------------------ BUG-ID: 28267 STATUS: Open/Postponed CATEGORY: Accuracy problem SUMMARY: poor convergence region for gsl_sf_hyperg_1F1 The magnitude of the error is greater than the value itself for a<<0, b>0, x>>0 gsl_sf_hyperg1F1(-3.78e+01, 2, 1.035e+02) => -7.00055e+18 +/- 3.77654e+19 ----------------------------------------------- From: Weibin Li <weibinli@mpipks-dresden.mpg.de> To: bug-gsl@gnu.org Subject: [Bug-gsl] gsl_sf_hyperg_1F1 Date: Mon, 30 Nov 2009 15:26:11 +0100 Hi, guys I experienced bugs with gsl_sf_hyperg_1F1. The version is gsl_1.12, but the testing is also done with gsl_1.13, using a mac with version 10.5.8 and hp-workstation with gnome_2.24.1. #include<stdlib.h> #include<stdio.h> #include<math.h> #include "gsl/gsl_sf_hyperg.h" int main(int argc, char **argv) { int ii; double Ri; double v0; gsl_sf_result r; for(ii = 10; ii< 140;ii++) { Ri = 2013; v0 =38.86871 +ii*2.5e-10; gsl_sf_hyperg_1F1_e(1.0-v0,2,2.0*Ri/v0,&r); printf("%lg\t%14.13g\t%14.13g\n",v0,r.val,r.err); } return 0; } The output of above code shows an extremely large error. by increasing Ri, the relative error decreases. Is there any idea to fix this? Thank you very much. Best Weibin -It's inherently difficult to compute the value in this region either way as there is massive cancellation in both the series and the Kummer transformed series.I cannot find any algorithm which handles this case.Confirmed ------------------------------------------------------------------------ BUG-ID: 21828 STATUS: Open/Confirmed CATEGORY: Performance SUMMARY: suboptimal performance of gsl_fdfsolver_lmsder From: "Alexander Usov" <a.s.usov@gmail.com> To: help-gsl@gnu.org Subject: [Help-gsl] Strange performance of gsl_fdfsolver_lmsder Date: Wed, 24 Oct 2007 20:45:01 +0200 Hi all, I am currently working on the problem involving source extraction from astronomical images, which essentially boils down to fitting a number of 2d gaussians to the image. One of the traditionally used fitters in this field is a Levenberg-Marquardt, which gsl_fdfsolver_lmsder is and implementation of. At some moment I have notices that for the bigger images (about 550 pixels, 20-30 parameters) gsl's lmsder algorithm spends a large fraction of the run-time (about 50%) doing household transform. While looking around for are different minimization algorithms I have made a surprising finding that original netlib/minpack/lmder is almost twice faster that that of gsl. Could anyone explain such a big difference in performace? -- Best regards, Alexander. _______________________________________________ Help-gsl mailing list Help-gsl@gnu.org http://lists.gnu.org/mailman/listinfo/help-gsl Reply-To: help-gsl@gnu.org From: Brian Gough <bjg@network-theory.co.uk> To: "Alexander Usov" <a.s.usov@gmail.com> Cc: help-gsl@gnu.org Subject: Re: [Help-gsl] Strange performance of gsl_fdfsolver_lmsder Date: Thu, 25 Oct 2007 21:57:08 +0100 At Wed, 24 Oct 2007 20:45:01 +0200, Alexander Usov wrote: > At some moment I have notices that for the bigger images (about 550 > pixels, 20-30 parameters) gsl's lmsder algorithm spends a large fraction > of the run-time (about 50%) doing household transform. > > While looking around for are different minimization algorithms I have made > a surprising finding that original netlib/minpack/lmder is almost twice faster > that that of gsl. > > Could anyone explain such a big difference in performace? I have a vague memory that there was some quantity (Jacobian?) that MINPACK only computes fully at the end, but in GSL it is accessible to the user at each step so I felt I had to update it on each iteration in the absence of some alternate scheme. Sorry this is not a great answer but I am not able to look at it in detail now. -- Brian Gough _______________________________________________ Help-gsl mailing list Help-gsl@gnu.org http://lists.gnu.org/mailman/listinfo/help-gsl 1824