Nikos: > Eigenvalue provided by i.pca. I can't nail this one: > > *** how is it calculated? *** Looks like it is some _weighted_ > > variance... !?? > .... > > Hamish, if you have the time (or anyone , could you please "translate" > > the code in "grass6_dev/imagery/i.pca/main.c", concerning the "eigval" > > variable, in some pseudocode. It is really the last thing to clarify ( I > > think ).
Hamish: > for i.pca they are calculated by the eigen() function in lib/gmath/eigen.c > see also lib/gmath/eigen_tools.c I am trying to get a grip on eigen.c. The variables that refer to the eigenvalues are symbolised as: double *lambda OR lambda which is the double d[] as defined IN G_tqli() IN eigen_tools.c And then there is this "fabs" in the way :-) I suppose it returns the absolute value of a signed number... It took me so long to figure this simple thing out. Well, there are so many variables... it's hard(=time-consuming) for the unexperienced eye to trace down the real math. As suggested by Markus, I will try to move this in the Wiki. Apologies for the long posts again, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
