Hi All- Jim Rohlf has already stated the reason for the problem here, CVA requires a division by a pooled covariance matrix estimated from your data. To avoid have a singularity in this matrix, you need a sample size larger than the degrees of freedom remaining in your variables.
The ideal approach to this is to get more data, but that may be difficult. I have a version of CVAGen that will first perform a PCA on the partial warp scrores and uniform components, and then perform a CVA on a limited number of the PCA scores. So if you have 20 variables in the data and only 20 specimens, you might find that the first 5 or 6 PCA axes have 90% or more of the variance, so that a CVA using only 5 or 6 PCA axes might might produce reasonable results. This approach may be particularly useful if you are using a lot of semi-landmarks. This version of CVAGen is on the page at http://www.canisius.edu/~sheets/moremorph.html under the New Two-D Software section, called PCA_CVA. It might prove helpful. I should put a test routine for this degrees of freedom issue and put a more informative error message into the program. In the second question below, I'm not sure what is happening. I assume the two data sets have the same numbers of landmarks? If you can send me a copy of the files, I can have a look and chase this down. -Dave H. David Sheets, PhD Chair,Dept of Physics, Canisius College 2001 Main St Buffalo NY 14208 ---- Original message ---- >Date: Tue, 13 Feb 2007 14:35:55 -0500 >From: morphmet <[EMAIL PROTECTED]> >Subject: Advice on IMP >To: morphmet <[email protected]> > >Hi everybody! >I am using geometric morphometrics in a study on mandibles of mice. I >have encountered problems using programs in the IMP series, and I would >be very grateful if somebody more experienced with these could give me a >hint on what to do here: > >1)I load an output file from CoordGen and a GroupList file into CVAGen. >The program displays the landmarks but does not finish the analysis, >instead posting an error message: The within-group sum of squares and >cross products matrix is singular. I have inspected both input files >several times; I cannot find any error; they do also perform well in >PCAGen. What does the message tell me about my data? > >2) I load two X1Y1CS format files into TwoGroup. The landmarks are >displayed and I can calculate Goodalls F. Anyway, when I click on F >test, Procrustes I am getting an error message saying that matrix >dimensions must agree. Why is this? What do I have to change? > >If anyone wishes to reply to me directly, my email address is: >[EMAIL PROTECTED] >Thank you very much and let me know if I can return you a favor. > >Louis > >_________________________________________________________________ >Haben Spinnen Ohren? Finden Sie es heraus mit dem MSN Suche Superquiz >via >http://www.msn-superquiz.de Jetzt mitmachen und gewinnen! > > > >-- >Replies will be sent to the list. >For more information visit http://www.morphometrics.org > -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
