On Sun, Nov 25, 2012 at 2:54 PM, Rafael Laboissiere <raf...@laboissiere.net> wrote: > The function cov2ellipse in the geometry package is not computing the > ellipse axes correctly. The first problem is that the scale of the axes is > wrong. This can be demonstrated with the code below > > ###################################################################### > function cov2ellipse_demo (K) > L = chol(K,'lower'); > u = randn(1e3,2)*L'; > elli = cov2ellipse (K); > figure(1) > plot(u(:,1),u(:,2),'.r'); > hold on; > drawEllipse(elli,'linewidth',2); > hold off; > axis tight; > endfunction > cov2ellipse_demo (K); ## This is what we get with "demo cov2ellipse" > cov2ellipse_demo (10*K); > cov2ellipse_demo (0.1*K); > ###################################################################### > > This is fixed by taking the square root of the eigenvalues obtained by > svd(). > > The second problem is that the axis orientation is wrong, evidenced in the > code below: > > ###################################################################### > K = [2 -1; -1 2]; > cov2ellipse_demo (K) > ###################################################################### > > This happens because the wrong elements of the eigenvectors are taken. > > The patch attached below fixes both problems. > > Rafael > > > ------------------------------------------------------------------------------ > Monitor your physical, virtual and cloud infrastructure from a single > web console. Get in-depth insight into apps, servers, databases, vmware, > SAP, cloud infrastructure, etc. Download 30-day Free Trial. > Pricing starts from $795 for 25 servers or applications! > http://p.sf.net/sfu/zoho_dev2dev_nov > _______________________________________________ > Octave-dev mailing list > Octave-dev@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/octave-dev >
Thank you again Rafael! I applied the patch. How did you find this bug? ------------------------------------------------------------------------------ Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
