spam (version 2.1-1)

spam operations: Basic Linear Algebra for Sparse Matrices

Description

Basic linear algebra operations for sparse matrices of class spam.

Details

Linear algebra operations for matrices of class spam are designed to behave exactly as for regular matrices. In particular, matrix multiplication, transpose, addition, subtraction and various logical operations should work as with the conventional dense form of matrix storage, as does indexing, rbind, cbind, and diagonal assignment and extraction (see for example diag). Further functions with identical behavior are dim and thus nrow, ncol.

The function norm calculates the (matrix-)norm of the argument. The argument type specifies the l1 norm, sup or max norm (default), or the Frobenius or Hilbert-Schmidt (frobenius/hs) norm. Partial matching can be used. For example, norm is used to check for symmetry in the function chol by computing the norm of the difference between the matrix and its transpose

The operator %d*% efficiently multiplies a diagonal matrix (in vector form) and a sparse matrix and is used for compatibility with the package fields. More specifically, this method is used in the internal functions of Krig to make the code more readable. It avoids having a branch in the source code to handle the diagonal or nondiagonal cases. Note that this operator is not symmetric: a vector in the left argument is interpreted as a diagonal matrix and a vector in the right argument is kept as a column vector.

The operator %d+% efficiently adds a diagonal matrix (in vector form) and a sparse matrix, similarly to the operator %d+%.

References

Some Fortran functions are based on http://people.sc.fsu.edu/~jburkardt/f_src/sparsekit/sparsekit.html

See Also

spam for coercion and other class relations involving the sparse matrix classes.

Examples

# NOT RUN {
# create a weight matrix and scale it:
# }
# NOT RUN {
wij <- distmat
# with distmat from a nearest.dist(..., upper=TRUE) call

n <- dim(wij)[1]

wij@entries <- kernel( wij@entries, h) # for some function kernel
wij <- wij + t(wij) + diag.spam(n)     # adjust from diag=FALSE, upper=TRUE

sumwij <- wij %*% rep(1,n)
    # row scaling:
    #   wij@entries <- wij@entries/sumwij[ wij@colindices]
    # col scaling:
wij@entries <- wij@entries/sumwij[ rep(1:n, diff(wij@rowpointers))]
# }