From georgi.boshnakov at manchester.ac.uk  Mon Nov 10 13:49:38 2014
From: georgi.boshnakov at manchester.ac.uk (Georgi Boshnakov)
Date: Mon, 10 Nov 2014 12:49:38 +0000
Subject: [Rd] ambiguity in the documented return value of Null() from
	package MASS
Message-ID: <438D2EC9EAFE5946B2D5864670EA468E0145C06617@MBXP01.ds.man.ac.uk>

Hi,
 
Function Null from package MASS seems to return a matrix with zero columns and the expected number of rows when
the null space of the argument contains only the zero vector, e.g. 

> library(MASS)
> diag(nrow=3)
     [,1] [,2] [,3]
[1,]    1    0    0
[2,]    0    1    0
[3,]    0    0    1

>  Null(diag(nrow=3))

[1,]
[2,]
[3,]

But the documentation of Null  seems to imply that the result is numeric(0):

-----------------------------------------------

Value: 

The matrix 'N' with the basis for the null space, or an empty
     vector if the matrix 'M' is square and of maximal rank.

-----------------------------------------------

(R version 3.1.1 Patched (2014-09-21 r66653) -- "Sock it to Me")

Georgi



[Rd] ambiguity in the documented return value of Null() from package MASS
Georgi Boshnakov