R/ctqwalk.R

In qwalkr: Handle Continuous-Time Quantum Walks with R

#' Create a Continuous-time Quantum Walk
#'
#' @description `ctqwalk()` creates a quantum walk object from a hamiltonian.
#'
#' @param hamiltonian  a Hermitian Matrix representing the Hamiltonian of the system.
#' @param ... further arguments passed on to [qwalkr::spectral()]
#'
#' @returns A list with the walk related objects, i.e the hamiltonian and its spectral
#'   decomposition (See [qwalkr::spectral()] for further details)
#'
#' @seealso [qwalkr::spectral()], [qwalkr::unitary_matrix.ctqwalk()],
#' [qwalkr::mixing_matrix.ctqwalk()], [qwalkr::avg_matrix.ctqwalk()],
#' [qwalkr::gavg_matrix.ctqwalk()]
#' @export
#'
#' @examples
#' # Creates a walk from the adjacency matrix of the graph P3.
#' ctqwalk(matrix(c(0,1,0,1,0,1,0,1,0), nrow=3))
#'
#'
ctqwalk <- function(hamiltonian, ...){
  if(!isSymmetric(hamiltonian)){
    stop("Hamiltonian must be a Hermitian matrix!")
  }

  output <- c(list(hamiltonian=hamiltonian), spectral(hamiltonian, ...))

  class(output) <- c("ctqwalk", "spectral")

  return (output)
}

#' Print the ctqwalk output
#'
#' @param x an object of the class ctqwalk.
#' @param ... further arguments passed to or from other methods.
#'
#' @returns Called mainly for its side effects. However, also
#'    returns `x` invisibly.
#' @export
print.ctqwalk <- function(x, ...){
  m <- length(x$multiplicity)

  sp <- rbind(round(x$eigvals, 2),
              round(x$multiplicity, 1))

  rownames(sp) <- c("Eigenvalue:", "Multiplicity:")
  colnames(sp) <- rep("", m)


  cat("Continuous-Time Quantum Walk\n\n")

  cat("[+]Order:", sum(x$multiplicity), "\n\n")

  cat("[+]Spectrum of the Hamiltonian:\n")

  print(sp)

  invisible(x)
}