rankMatrix  R Documentation 
Compute ‘the’ matrix rank, a welldefined functional in theory(*), somewhat ambiguous in practice. We provide several methods, the default corresponding to Matlab's definition.
(*) The rank of a n \times m
matrix A
, rk(A)
,
is the maximal number of linearly independent columns (or rows); hence
rk(A) \le min(n,m)
.
rankMatrix(x, tol = NULL,
method = c("tolNorm2", "qr.R", "qrLINPACK", "qr",
"useGrad", "maybeGrad"),
sval = svd(x, 0, 0)$d, warn.t = TRUE, warn.qr = TRUE)
qr2rankMatrix(qr, tol = NULL, isBqr = is.qr(qr), do.warn = TRUE)
x 
numeric matrix, of dimension 
tol 
nonnegative number specifying a (relative,
“scalefree”) tolerance for testing of
“practically zero” with specific meaning depending on

method 
a character string specifying the computational method for the rank, can be abbreviated:

sval 
numeric vector of nonincreasing singular values of

warn.t 
logical indicating if 
warn.qr 
in the 
qr 
an R object resulting from 
isBqr 

do.warn 
logical; if true, warn about nonfinite diagonal
entries in the 
qr2rankMatrix()
is typically called from rankMatrix()
for
the "qr"
* method
s, but can be used directly  much more
efficiently in case the qr
decomposition is available anyway.
If x
is a matrix of all 0
(or of zero dimension), the rank
is zero; otherwise, typically a positive integer in 1:min(dim(x))
with attributes detailing the method used.
There are rare cases where the sparse QR
decomposition
“fails” in so far as the diagonal entries of R
, the
d_i
(see above), end with nonfinite, typically NaN
entries. Then, a warning is signalled (unless warn.qr
/
do.warn
is not true) and NA
(specifically,
NA_integer_
) is returned.
For large sparse matrices x
, unless you can specify
sval
yourself, currently method = "qr"
may
be the only feasible one, as the others need sval
and call
svd()
which currently coerces x
to a
denseMatrix
which may be very slow or impossible,
depending on the matrix dimensions.
Note that in the case of sparse x
, method = "qr"
, all
nonstrictly zero diagonal entries d_i
where counted, up to
including Matrix version 1.10, i.e., that method implicitly
used tol = 0
, see also the set.seed(42)
example below.
Martin Maechler; for the "*Grad" methods building on suggestions by Ravi Varadhan.
qr
, svd
.
rankMatrix(cbind(1, 0, 1:3)) # 2
(meths < eval(formals(rankMatrix)$method))
## a "border" case:
H12 < Hilbert(12)
rankMatrix(H12, tol = 1e20) # 12; but 11 with default method & tol.
sapply(meths, function(.m.) rankMatrix(H12, method = .m.))
## tolNorm2 qr.R qrLINPACK qr useGrad maybeGrad
## 11 11 12 12 11 11
## The meaning of 'tol' for method="qrLINPACK" and *dense* x is not entirely "scale free"
rMQL < function(ex, M) rankMatrix(M, method="qrLINPACK",tol = 10^ex)
rMQR < function(ex, M) rankMatrix(M, method="qr.R", tol = 10^ex)
sapply(5:15, rMQL, M = H12) # result is platform dependent
## 7 7 8 10 10 11 11 11 12 12 12 {x86_64}
sapply(5:15, rMQL, M = 1000 * H12) # not identical unfortunately
## 7 7 8 10 11 11 12 12 12 12 12
sapply(5:15, rMQR, M = H12)
## 5 6 7 8 8 9 9 10 10 11 11
sapply(5:15, rMQR, M = 1000 * H12) # the *same*
## "sparse" case:
M15 < kronecker(diag(x=c(100,1,10)), Hilbert(5))
sapply(meths, function(.m.) rankMatrix(M15, method = .m.))
#> all 15, but 'useGrad' has 14.
sapply(meths, function(.m.) rankMatrix(M15, method = .m., tol = 1e7)) # all 14
## "large" sparse
n < 250000; p < 33; nnz < 10000
L < sparseMatrix(i = sample.int(n, nnz, replace=TRUE),
j = sample.int(p, nnz, replace=TRUE),
x = rnorm(nnz))
(st1 < system.time(r1 < rankMatrix(L))) # warning+ ~1.5 sec (2013)
(st2 < system.time(r2 < rankMatrix(L, method = "qr"))) # considerably faster!
r1[[1]] == print(r2[[1]]) ## > ( 33 TRUE )
## another sparse"qr" one, which ``failed'' till 20131123:
set.seed(42)
f1 < factor(sample(50, 1000, replace=TRUE))
f2 < factor(sample(50, 1000, replace=TRUE))
f3 < factor(sample(50, 1000, replace=TRUE))
D < t(do.call(rbind, lapply(list(f1,f2,f3), as, 'sparseMatrix')))
dim(D); nnzero(D) ## 1000 x 150 // 3000 nonzeros (= 2%)
stopifnot(rankMatrix(D, method='qr') == 148,
rankMatrix(crossprod(D),method='qr') == 148)
## zero matrix has rank 0 :
stopifnot(sapply(meths, function(.m.)
rankMatrix(matrix(0, 2, 2), method = .m.)) == 0)
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