From sokol at insa-toulouse.fr  Thu Jan 18 16:13:43 2018
From: sokol at insa-toulouse.fr (Serguei Sokol)
Date: Thu, 18 Jan 2018 16:13:43 +0100
Subject: [Rd] wrong matrix dimension in sparseQR
Message-ID: <55e71a12-c542-3488-7ed7-88a25b0e3b51@insa-toulouse.fr>

Hi,

I came across a case when the dimensions of matrices returned by qr()
operated on a sparse matrix does not coincide with the initial matrix.

Here is a spinet code that should produce an example (one of many that I could provide):

 ?m=205
 ?n=199
 ?set.seed(7);
 ?a=matrix(rnorm(m*n), m, n)
 ?a[sample(seq(m*n), m*(n-4))]=0
 ?a=as(a, "Matrix")
 ?qa=qr(a);
 ?stopifnot(nrow(qa at R) == m)
 ?# On my box I have nrow(qa at R):=207 while should be 205 as m is)

Note that for m=203 and n=197, the same code produce right (i.e. coinciding) dimensions.

Have I missed something?

Serguei.

 > R.version
platform?????? x86_64-pc-linux-gnu
arch?????????? x86_64
os???????????? linux-gnu
system???????? x86_64, linux-gnu
status
major????????? 3
minor????????? 4.3
year?????????? 2017
month????????? 11
day??????????? 30
svn rev??????? 73796
language?????? R
version.string R version 3.4.3 (2017-11-30)
nickname?????? Kite-Eating Tree



[Rd] wrong matrix dimension in sparseQR
Serguei Sokol