[R] Reconstructing LD function

usenet@s-boehringer.de usenet at s-boehringer.de
Fri Jul 1 15:29:26 CEST 2005

On Mon, 2005-06-27 at 13:18, Prof Brian Ripley wrote:
> On Mon, 27 Jun 2005 usenet at s-boehringer.de wrote:
> > in an LDA analysis with n groups n-1 LD functions result. Implicitly this
> > defines an LD fucntion for the last group. Does there exist code already
> > to explictly construct this LD function?

Thank you for the quick reply.

> What `LDA analysis' are our discussing here?  (LDA is usually
> `linear discriminant analysis', so what did you mean and what R function
> are you nor referring to?)

> R has lda in package MASS, and that works with n LD functions.  To reduce
> it to n-1, subtract the last one from the others, in which case LD_n == 0.
Indeed I have been using the MASS::lda package.

> Anything you do in LD analysis only depends on differences in LD
> functions, and there really are n of them.  With two groups one is
> conventionally taken to be zero (the first, usually, not the last).
How is the classifcation decision reached from the LD functions? Are
those what is known as "linear Fisherian discriminant functions"? If so,
I'm not positive about why one of these functions can be set to 0.

Thank you in advance for the clarification.

Best wishes,


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