band {Matrix} | R Documentation |
Return the matrix obtained by setting to zero elements below a diagonal
(triu
), above a diagonal (tril
), or outside of a general
band (band
).
band(x, k1, k2, ...)
triu(x, k = 0, ...)
tril(x, k = 0, ...)
x |
a matrix-like object |
k,k1,k2 |
integers specifying the diagonals that are not set to
zero. These are interpreted relative to the main diagonal, which
is |
... |
optional arguments passed methods (currently unused by package Matrix) |
triu(x, k)
is equivalent to band(x, k, dim(x)[2])
.
Similarly,
tril(x, k)
is equivalent to band(x, -dim(x)[1], k)
.
An object of a suitable matrix class, inheriting from
triangularMatrix
where appropriate.
It inherits from sparseMatrix
if
and only if x
does.
method for compressed, sparse, column-oriented matrices.
method for compressed, sparse, row-oriented matrices.
method for sparse matrices in triplet format.
method for diagonal matrices.
method for dense matrices in packed or unpacked format.
method for traditional matrices
of implicit class matrix
.
bandSparse
for the construction of a
banded sparse matrix directly from its non-zero diagonals.
## A random sparse matrix :
set.seed(7)
m <- matrix(0, 5, 5)
m[sample(length(m), size = 14)] <- rep(1:9, length=14)
(mm <- as(m, "CsparseMatrix"))
tril(mm) # lower triangle
tril(mm, -1) # strict lower triangle
triu(mm, 1) # strict upper triangle
band(mm, -1, 2) # general band
(m5 <- Matrix(rnorm(25), ncol = 5))
tril(m5) # lower triangle
tril(m5, -1) # strict lower triangle
triu(m5, 1) # strict upper triangle
band(m5, -1, 2) # general band
(m65 <- Matrix(rnorm(30), ncol = 5)) # not square
triu(m65) # result not "dtrMatrix" unless square
(sm5 <- crossprod(m65)) # symmetric
band(sm5, -1, 1)# "dsyMatrix": symmetric band preserves symmetry property
as(band(sm5, -1, 1), "sparseMatrix")# often preferable
(sm <- round(crossprod(triu(mm/2)))) # sparse symmetric ("dsC*")
band(sm, -1,1) # remains "dsC", *however*
band(sm, -2,1) # -> "dgC"