Simple function for computing the trace of a square matrix. Should replicate the output of sum(diag(matrix)).

matrix_trace.R

# Simple function for computing the trace of a matrix. Should replicate the output of sum(diag(matrix)).
# Function requires a square n x n matrix as input.
# Used in post demonstrating the trace of a matrix here: http://wp.me/p4aZEo-5Nb


trace <- function(A) {
  n <- dim(A)[1] # get dimension of matrix
  
  # Check that the matrix is square
  if (n != dim(A)[2]) {
    stop('Matrix is not square')
  }
  tr <- 0 # initialize trace value
  
  # Loop over the diagonal elements of the supplied matrix and add the element to tr
  for (k in 1:n) {
    l <- A[k,k]
    tr <- tr + l
  }
  
  return(tr[[1]])
}