R/20_eigs_real_sym.R

In RSpectra: Solvers for Large-Scale Eigenvalue and SVD Problems

eigs_real_sym <- function(A, n, k, which, sigma, opts, mattype, extra_args = list())
{
    # Check whether 'A' is a square matrix
    # Skip this step if A is a function
    if (!is.null(dim(A)))
    {
        if (nrow(A) != ncol(A) | nrow(A) != n)
            stop("'A' must be a square matrix of size n")
    }

    # eigs() is not suitable for small matrices
    if (n < 3)
        stop("dimension of 'A' must be at least 3")

    # If all eigenvalues are requested, call eigen() instead,
    # and give a warning
    if (k == n)
    {
        warning("all eigenvalues are requested, eigen() is used instead")
        return(c(eigen(if(extra_args$use_lower) A else t(A),
                       symmetric = TRUE,
                       only.values = identical(opts$retvec, FALSE)),
                 nconv = n, niter = 0))
    }

    # Matrix will be passed to C++, so we need to check the type.
    # Convert the matrix type if A is stored other than double.
    #
    # However, for dsyMatrix matrices defined in Matrix package,
    # they are always double, so we can omit this check.
    if (mattype == "matrix" & typeof(A) != "double")
    {
        mode(A) = "double"
    }
    # Check the value of 'k'
    if (k <= 0 | k >= n)
        stop("'k' must satisfy 0 < k < nrow(A)")

    # Check sigma
    if (is.null(sigma))
    {
        workmode = "regular"
        sigma = 0
    } else {
        workmode = "real_shift"
        if(is.complex(sigma)) warning("only real part of sigma is used")
        sigma = Re(sigma)
    }

    # Arguments to be passed to Spectra
    spectra.param = list(which = which,
                         ncv = min(n, max(2 * k + 1, 20)),
                         tol = 1e-10,
                         maxitr = 1000,
                         retvec = TRUE,
                         user_initvec = FALSE,
                         sigma = sigma)

    # Check the value of 'which'
    eigenv.type = c("LM", "SM", "LA", "SA", "BE")
    if (!(spectra.param$which %in% eigenv.type))
    {
        stop(sprintf("argument 'which' must be one of\n%s",
                     paste(eigenv.type, collapse = ", ")))
    }

    # Update parameters from 'opts' argument
    spectra.param[names(opts)] = opts
    spectra.param$which = EIGS_RULE[spectra.param$which]

    # Any other arguments passed to C++ code, for example use_lower and fun_args
    spectra.param = c(spectra.param, as.list(extra_args))

    # Check the value of 'ncv'
    if (spectra.param$ncv <= k | spectra.param$ncv > n)
        stop("'opts$ncv' must be > k and <= nrow(A)")

    # Check the value of 'initvec'
    if ("initvec" %in% names(spectra.param))
    {
        if(length(spectra.param$initvec) != n)
            stop("'opt$initvec' must have length n")
        spectra.param$initvec = as.numeric(spectra.param$initvec)
        spectra.param$user_initvec = TRUE
    }

    # Call the C++ function
    fun = switch(workmode,
                 regular = "eigs_sym",
                 real_shift = "eigs_shift_sym",
                 stop("unknown work mode"))
    dot_call_args = list(
        fun,
        A, as.integer(n), as.integer(k), as.list(spectra.param), as.integer(MAT_TYPE[mattype]),
        PACKAGE = "RSpectra"
    )
    do.call(.Call, args = dot_call_args)
}