>I'm rusty, but not *that* rusty here, I hope. > >If W (=Z*Z' in your case) is singular, it can not have >inverse, which by >definition also mean that nothing multiply by it will >produce the identity >matrix (for otherwise it would have an inverse and >thus nonsingular). > >The definition of a generalized inverse is something >like: If A is a >non-null matrix, and G satisfy AGA = A, then G is >called a generalized >inverse of A. This is not unique, but a unique one >that satisfy some >additional properties is the Moore-Penrose inverse. I >don't know if this is >what ginv() in MASS returns, as I have not used it >before.
Andy The inverse of a Matrix A is defined as a Matrix B such that B*A=A*B=I and not just B*A=I. But there are matrices B for singular matrices A such that B*A=I but A*B != I, therefore there exist "left-inverses" (or "right-inverses") for non-invertable matrices. Best Regards __________________________________ Yahoo! Finance: Get your refund fast by filing online. ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
